Diploid germ cells produce haploid gametes through meiosis, a unique type of cell division. Independent reassortment of parental chromosomes and their recombination leads to ample genetic variability among the gametes. Importantly, new mutations also occur during meiosis, at frequencies much higher than during the mitotic cell cycles. These meiotic mutations are associated with genetic recombination and depend on double‐strand breaks (DSBs) that initiate crossing over. Indeed, sequence variation among related strains is greater around recombination hotspots than elsewhere in the genome, (...) presumably resulting from recombination‐associated mutations. Significantly, enhanced mutagenicity in meiosis may lead to faster divergence during evolution, as germ‐line mutations are the ones that are transmitted to the progeny and thus have an evolutionary impact. The molecular basis for mutagenicity in meiosis may be related to the repair of meiotic DSBs by polymerases, or to the exposure of single‐strand DNA to mutagenic agents during its repair. (shrink)

Brazil is the biggest market for pesticides in the world. In the registration process, a pesticide must be authorized by the Institute of the Environment, Health Surveillance Agency and Ministry of Agriculture. Evaluations follow a package of toxicological studies submitted by the companies and also based on the Brazilian law regarding pesticides. We confronted data produced by private laboratories, submitted to the Institute of the Environment for registration, with data obtained from scientific databases, corresponding to mutagenicity, carcinogenicity and teratogenicity of (...) pesticides. All studies submitted by the companies were carried out by private laboratories. From 247 pesticide formulations analyzed, none showed positive results for mutagenicity, carcinogenicity or teratogenicity. From 574 articles in the scientific literature, 84% published by public laboratories showed positive results, while 79% of those showing negative results came from private laboratories. There is an ethical concern about a conflict of interest between public/independent laboratories and private laboratories that produce data for registering pesticides. We demonstrated that there is a clear contradiction between public and private laboratories. Brazilian regulatory authorities have approved the registration of pesticides based almost exclusively on the monographs provided by the pesticide industry, because the use of scientific articles or information from the independent literature is strongly belittled by the industry. Pesticide companies argue that scientific articles cannot be trusted. Also, according to the industry, pesticide registration cannot be refused based on results from scientific articles. Thus, the registration of pesticides with mutagenic, carcinogenic and teratogenic risks has been approved in Brazil. (shrink)

The replicative bypass of lesions in DNA and the induction of mutations by agents which react with DNA to produce damaged bases can be understood on the basis of a simple kinetic model. Bypass can be analyzed by separately considering three processes: (a) addition of a base opposite a lesion, (b) a proofreading excision process, and (c) a rate limiting elongation step. Adenine nucleotides are preferentially added opposite many lesions making it possible to predict mutational specificity. Replicative bypass (translesion synthesis) (...) is dependent on modulation of proofreading exonuclease activity but loss of exonuclease activity alone is not sufficient to ensure bypass. Frameshift mutation is the result of the failure of translesion synthesis accompanied by rearrangement of the template, particularly at repetitive sites. (shrink)

Exocyclic DNA adducts are mutagenic lesions that can be formed by both exogenous and endogenous mutagens/carcinogens. These adducts are structurally analogs but can differ in certain features such as ring size, conjugation, planarity and substitution. Although the information on the biological role of the repair activities for these adducts is largely unknown, considerable progress has been made on their reaction mechanisms, substrate specificities and kinetic properties that are affected by adduct structures. At least four different mechanisms appear to have (...) evolved for the removal of specific exocyclic adducts. These include base excision repair, nucleotide excision repair, mismatch repair, and AP endonuclease‐mediated repair. This overview highlights the recent progress in such areas with emphasis on structure–activity relationships. It is also apparent that more information is needed for a better understanding of the biological and structural implications of exocyclic adducts and their repair. BioEssays 26:1195–1208, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

Somatic diversification of antigen receptor genes depends on the activity of enzymes whose homologs participate in a mutagenic DNA repair in unicellular species. Indeed, by engaging error-prone polymerases, gap filling molecules and altered mismatch repair pathways, lymphocytes utilize conserved components of genomic stress response systems, which can already be found in bacteria and archaea. These ancient systems of mutagenesis and repair act to increase phenotypic diversity of microbial cell populations and operate to enhance their ability to produce fit variants during (...) stress. Coopted by lymphocytes, the ancient mutagenic processing systems retained their diversification functions instilling the adaptive immune cells with enhanced evolvability and defensive capacity to resist infection and damage. As reviewed here, the ubiquity and conserved character of specialized variation-generating mechanisms from bacteria to lymphocytes highlight the importance of these mechanisms for evolution of life in general. (shrink)

Several DNA-damage detection and repair mechanisms have evolved to repair double-strand breaks induced by mutagens. Later in evolutionary history, DNA single- and double-strand cuts made possible immune diversity by V(D)J recombination and recombination at meiosis. Such cuts are induced endogenously and are highly regulated and controlled. In meiosis, DNA cuts are essential for the initiation of homologous recombination, and for the formation of joint molecule and crossovers. Many proteins that function during somatic DNA-damage detection and repair are also active (...) during homologous recombination. However, their meiotic functions may be altered from their somatic roles through localization, posttranslational modifications and/or interactions with meiosis-specific proteins. Presumably, somatic repair functions and meiotic recombination diverged during evolution, resulting in adaptations specific to sexual reproduction. BioEssays 27:795–808, 2005. © 2005 Wiley Periodicals, Inc. (shrink)

In lieu of an abstract, here is a brief excerpt of the content:The Human Genome Project and BioethicsEric T. Juengst, Ph.D. (bio)The fifteen-year "human genome project" at the National Institutes of Health and the Department of Energy officially began on October 1, 1990. With it began a new dimension in federally supported scientific research: concurrent funding for work to anticipate the social consequences of the project's research and to develop policies to guide the use of the knowledge it produces. As (...) a result, the National Center for Human Genome Research (NCHGR) at NIH will support the largest public investment in bioethical analysis to date.NCHGR was established to work with other federal, private, and international organizations on the scientific effort to characterize the form and content of the human genome. The research will yield information—high-resolution genetic linkage and physical maps of all the human chromosomes as well as human DNA sequence data—that will be a resource for studies of gene structure and function. It will greatly increase our understanding of the genetic aspects of human health and disease. That increased understanding will eventually provide insights into the prevention and treatment of the 3,000 known inherited disorders, and of conditions caused by our (gene-governed) physiological reactions to pathogens, toxins, and mutagens of external origin.It has been clear since the conception of the human genome project, however, that professional and public deliberations concerning the responsible use of genetic information must be a part of the process. The most immediate consequence of genome research will be the development of new diagnostic and predictive tests, well in advance of corresponding therapeutic or curative advances. The implications of acquiring and using that knowledge about individuals raise policy questions at many levels within society. The primary purpose of the Ethical, Legal and Social Implications Program at the NCHGR is to anticipate and address these questions early in the life of the scientific project, to help optimize the [End Page 71] benefits to human welfare and opportunity from the new knowledge, and to guard against its misuses.The program has identified three sets of questions as particularly important to pursue as the genome initiative proceeds:1.Issues involved in the integration of new genetic tests into medical practice. Human genome research is expected to increase greatly the number of gene-based diagnostic and prognostic tests available to health professionals. The bioethical policy problems involved in integrating those tests effectively into medical practice include developing standards for:— accuracy and quality control of genetic tests;— medical indications for testing and design of testing protocols;— professional responsibilities of clinicians who perform tests;— confidentiality of information obtained from testing;— access to and use of test results by third parties, such as health insurers; and— reimbursement for testing and test-related counseling.These are problems for both those charged with regulating the use of new genetic tests and for those establishing the standards of practice within the health professions. Thus, in addition to soliciting and funding scholarly research proposals on both the factual and normative questions raised by these problems, the program is commissioning a major new study by the National Academy of Sciences/Institute of Medicine aimed at providing professional guidelines for the integration of genetic services into mainstream medical practice.2. Issues involved in educating and counseling individuals about genetic test results. The primary risk that health professionals will face in using genetic tests is the misinterpretation of their findings and the resulting potential for psychological trauma, stigmatization, and discrimination. Sometimes, out of ignorance, patients, families, and social institutions already stigmatize genetic disorders and treat those with them unfairly. This risk broadens as the genetic elements of more health problems are uncovered and gene-based tests for susceptibilities and carrier states are developed.To protect against these risks, NCHGR is soliciting and supporting projects aimed at improving professional and public understanding of these tests and their implications. For example, a philosopher is leading a team of geneticists and physicians in a scholarly effort to clarify [End Page 72] concepts of genetic susceptibility and draw out the social meaning of their different interpretations. Other projects involve social scientific studies of genetic risk perceptions, stigmatization, and discrimination. The conclusions of these studies, and... (shrink)

That cacophony you hear is coming from the growing number of commentators addressing ethical, social, and policy issues raised by nanotechnology. Like many novel technologies that disturb the status quo, nanotechnologies raise questions about the adequacy of oversight systems; the extent to which the technologies push legal, moral, and political boundaries; and ultimately, the implications for human health and well-being. Because nanoscale techniques and products challenge our ways of thinking about biology, physics, and chemistry, nanotechnology forces us to reconsider accepted (...) wisdom on toxicity, mutagenicity, contamination, biocompatibility, and other interactions among humans, the environment, and technologies. The sheer scale and reach of nanotechnologies demands institutions, collaborations, and conventions that can cross-link knowledge across organizations, disciplines, and locales. If ever there was an occasion to rethink the limits of disciplinary-specific knowledge, norms about regulatory processes, and societal implications of new technologies, nanotechnologies provide the opportunity. (shrink)

Here we present and develop the hypothesis that the derepression of endogenous retrotransposable elements (RTEs) – “genomic parasites” – is an important and hitherto under‐unexplored molecular aging process that can potentially occur in most tissues. We further envision that the activation and continued presence of retrotransposition contribute to age‐associated tissue degeneration and pathology. Chromatin is a complex and dynamic structure that needs to be maintained in a functional state throughout our lifetime. Studies of diverse species have revealed that chromatin undergoes (...) extensive rearrangements during aging. Cellular senescence, an important component of mammalian aging, has recently been associated with decreased heterochromatinization of normally silenced regions of the genome. These changes lead to the expression of RTEs, culminating in their transposition. RTEs are common in all kingdoms of life, and comprise close to 50% of mammalian genomes. They are tightly controlled, as their activity is highly destabilizing and mutagenic to their resident genomes. (shrink)

The DNA of all species is constantly under threat from both endogenous and exogenous factors, which damage its chemical structure. Probably the most common lesion that arises in cellular DNA is the loss of a base to generate an abasic site, which is usually referred to as an apurinic or apyrimidinic (AP) site. Since these lesions are potentially both cytotoxic and mutagenic, cells of all organisms express dedicated repair enzymes, termed AP endonucleases, to counteract their damaging effects. Indeed, many organisms (...) consider it necessary to express two or more of these lesion‐specific endonucleases, underscoring the requirement that exists to remove AP sites for the maintenance of genome integrity and cell viability. Most AP endonucleases are very versatile enzymes, capable of performing numerous additional repair roles. In this article, we review the AP endonuclease class of repair enzymes, with emphasis on the evolutionary conservation of structural features, not only between prokaryotic and eukaryotic homologues, but also between these enzymes and the RNase H domain of one class of reverse transcriptase. (shrink)

Here, we review genomic target site selection during retroviral integration as a multistep process in which specific biases are introduced at each level. The first asymmetries are introduced when the virus takes a specific route into the nucleus. Next, by co‐opting distinct host cofactors, the integration machinery is guided to particular chromatin contexts. As the viral integrase captures a local target nucleosome, specific contacts introduce fine‐grained biases in the integration site distribution. In vivo, the established population of proviruses is subject (...) to both positive and negative selection, thereby continuously reshaping the integration site distribution. By affecting stochastic proviral expression as well as the mutagenic potential of the virus, integration site choice may be an inherent part of the evolutionary strategies used by different retroviruses to maximise reproductive success. (shrink)

RNA polymerase II is recruited to DNA double‐strand breaks (DSBs), transcribes the sequences that flank the break and produces a novel RNA type that has been termed damage‐induced long non‐coding RNA (dilncRNA). DilncRNAs can be processed into short, miRNA‐like molecules or degraded by different ribonucleases. They can also form double‐stranded RNAs or DNA:RNA hybrids. The DNA:RNA hybrids formed at DSBs contribute to the recruitment of repair factors during the early steps of homologous recombination (HR) and, in this way, contribute to (...) the accuracy of the DNA repair. However, if not resolved, the DNA:RNA hybrids are highly mutagenic and prevent the recruitment of later HR factors. Here recent discoveries about the synthesis, processing, and degradation of dilncRNAs are revised. The focus is on RNA clearance, a necessary step for the successful repair of DSBs and the aim is to reconcile contradictory findings on the effects of dilncRNAs and DNA:RNA hybrids in HR. (shrink)

Endo‐exonucleases from E. coli to man, although very different proteins, are multifunctional enzymes with similar enzymatic activities. They probably have two common but opposing biological roles. On the one hand, they promote survival of the organism by acting in recombination and recombinational DNA repair to diversify and help preserve the genome intact. On the other hand, they degrade the genomic DNA when it is damaged beyond repair. This ensures elimination of heavily mutagenized cells from the population.

This personal account traces a series of studies that led from DNA physical chemistry to anticancer drug mechanisms. Chemical crosslinking as a basis for anticancer drug actions had been suspected since the time of the first clinical reports of the effectiveness of nitrogen mustard in 1946. After the elucidation of the DNA helix‐coil transition, several nearly concurrent findings in the early 1960s established the paradigm of DNA interstrand crosslinking. The DNA filter elution phenomenon was discovered in the early 1970s, and (...) lent itself to the development of practical assays for DNA crosslinks and other DNA lesions in mammalian cells. The assays allowed studies of the effects of DNA damaging agents at pharmacologically or toxicologically relevant doses, and have been widely applied in studies of mutagenic and chemotherapeutic agents. During the period 1979–1986, DNA filter elution studies led to the paradigm of DNA topoisomerases as targets of anticancer drug action, and this has become one of the most active areas of anticancer drug development. (shrink)

In this review, we discuss how two evolutionarily conserved pathways at the interface of DNA replication and repair, template switching and break-induced replication, lead to the deleterious large-scale expansion of trinucleotide DNA repeats that cause numerous hereditary diseases. We highlight that these pathways, which originated in prokaryotes, may be subsequently hijacked to maintain long DNA microsatellites in eukaryotes. We suggest that the negative mutagenic outcomes of these pathways, exemplified by repeat expansion diseases, are likely outweighed by their positive role in (...) maintaining functional repetitive regions of the genome such as telomeres and centromeres. Break-induced replication and template switching are conserved mechanisms of replication fork restart. They do not cause microsatellite instability in prokaryotes, but promote repeat expansion in eukaryotes. We suggest that TS and BIR persisted in eukaryotes despite their mutagenic potential because they help maintain long repetitive telomeres and centromeres. (shrink)

Recent mutagenesis studies have demonstrated that the chemotherapeutic agent, chlorambucll (CHL), is highly mutagenic in male germ cells of the mouse. Post‐melotic germ cells, and especially early spermatids, are the most sensitive to the cytotoxic and mutagenic effects of this agent. Genetic, cytogenetic and molecular analyses of many induced mutations have shown that, in these germ‐cell stages, CHL induces predominantly chromosomal rearrangements (deletions and translocations), and mutation‐rate studies show that, in terms of tolerated doses, CHL is perhaps five to ten (...) times more efficient in inducing rearrangements than is radiation exposure. Appropriate breeding protocols, along with knowledge of the advantages and limitations associated with the use of CHL, can be used to expand the current resource of chromosomal rearrangements in the mouse and to provide new phenotype‐associated mutations amenable to positional‐cloning techniques. The analysis of CHL‐induced mutations has also contributed to understanding the factors that affect the yield and nature of chemically induced germline mutations in mammals. (shrink)

Small tandem DNA duplications in the range of 15 to 300 base‐pairs play an important role in the aetiology of human disease and contribute to genome diversity. Here, we discuss different proposed mechanisms for their occurrence and argue that this type of structural variation mainly results from mutagenic repair of chromosomal breaks. This hypothesis is supported by both bioinformatical analysis of insertions occurring in the genome of different species and disease alleles, as well as by CRISPR/Cas9‐based experimental data from different (...) model systems. Recent work points to fill‐in synthesis at double‐stranded DNA breaks with complementary sequences, regulated by end‐joining mechanisms, to account for small tandem duplications. We will review the prevalence of small tandem duplications in the population, and we will speculate on the potential sources of DNA damage that could give rise to this mutational signature. With the development of novel algorithms to analyse sequencing data, small tandem duplications are now more frequently detected in the human genome and identified as oncogenic gain‐of‐function mutations. Understanding their origin could lead to optimized treatment regimens to prevent therapy‐induced activation of oncogenes and might expose novel vulnerabilities in cancer. (shrink)

In postmitotic neurons, nucleosomal turnover was long considered to be a static process that is inconsequential to transcription. However, our recent studies in human and rodent brain indicate that replication‐independent (RI) nucleosomal turnover, which requires the histone variant H3.3, is dynamic throughout life and is necessary for activity‐dependent gene expression, synaptic connectivity, and cognition. H3.3 turnover also facilitates cellular lineage specification and plays a role in suppressing the expression of heterochromatic repetitive elements, including mutagenic transposable sequences, in mouse embryonic stem (...) cells. In this essay, we review mechanisms and functions for RI nucleosomal turnover in brain and present the hypothesis that defects in histone dynamics may represent a common mechanism underlying neurological aging and disease. -/- . (shrink)

Oxycholesterols (OS) are formed from cholesterol or its immediate precursors by enzymatic or free radical action in vivo, or they may be derived from food. OS exhibit a wide spectrum of biological activities. In OS cytotoxicity, several mechanisms seem to be involved: e.g. inhibition of HMG‐CoA reductase activity, antiproliferative action, apoptosis induction, replacement of cholesterol by OS in membranes followed by changes in cellular membrane structure and functionality, and immune system functions alteration. Furthermore, OS may be mutagenic and carcinogenic and (...) may serve as intracellular signaling or regulatory molecules. Here we review OS cellular activities with special attention to the cytotoxic action in vivo and in vitro using experimental models. BioEssays 28: 387–398, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

Since the practice turn, the role technologies play in the production of scientific knowledge has become a prominent topic in science studies. Much existing scholarship, however, either limits technology to merely mechanical instrumentation or uses the term for a wide variety of items. This article argues that technologies in scientific practice can be understood as a result of past scientific knowledge becoming sedimented in materials, like model organisms, synthetic reagents or mechanical instruments, through the routine use of these materials in (...) subsequent research practice. The proposed theoretical interpretation of technology is examined through a case where a model organism—Drosophila melanogaster—acted as a technology for investigating a contested biological effect of a mechanical instrument: Hermann J. Muller’s experiments on X-ray mutagenicity in the 1920s. The article reconstructs how Muller employed two synthetic Drosophila stocks as tests for measuring X-rays’ capacity to cause genetic aberration. It argues that past scientific knowledge sedimented in the Drosophila stocks influenced Muller’s perception of X-ray-induced mutation. It further describes how Muller’s concept of X-ray mutagenicity sedimented through the adoption of X-ray machines as a ready-made resource for producing mutants by other geneticists, for instance George Beadle and Edward Tatum in their experiments on Neurospora crassa, despite ongoing disputes surrounding Muller’s conclusions. Technological sedimentation is proposed as a potential explanation why sedimentation and disputation may often coexist in the history of science. (shrink)

There is growing evidence that mutations can arise in non‐dividing cells (both bacterial and mammalian) in the absence of chromosomal replication. The processes that are involved are still largely unknown but may include two separate mechanisms. In the first, DNA lesions resulting from the action of endogenous mutagens may give rise to RNA transcripts with miscoded bases. If these confer the ability to initiate DNA replication, the DNA lesions may have an opportunity to miscode during replication and thus could (...) give rise to apparently ‘adaptive’ mutations. A second mechanism is suggested by recent work in starved bacteria, showing that there is much more turnover of chromosomal DNA than has been previously thought. This could permit polymerase errors to lead to mutations in non‐dividing cells. Such cryptic DNA synthesis, which may essentially replace existing DNA rather than duplicating it, could, in principle, act as an additional source of variability on which selection may act, initially in the absence of cell division. In mammals such processes would undoubtedly have implications for germ cell mutagenesis and carcinogenesis. (shrink)

Exposure of man to chemical agents can occur intentionally, as in the treatment of disease, or inadvertently because the environment contains a wide range of synthetic or naturally occurring chemicals. The alkylating agents are a diverse group of compounds (Fig. 1) and comprise a good example of such xenobiotics, since much is known about their occurrence, and their biological effects include carcinogenicity, mutagenicity, toxicity and teratogenicity.Exposure to potentially carcinogenic alkylating agents such as nitrosamines may occur occupationally, from cigarette smoke, from (...) certain foodstuffs and even endogenously through the ingestion of the appropriate precursor chemicals.1 At the other extreme, the cytotoxic effects of agents such as the chloroethylating nitrosamides or mustards have been exploited in the design of certain antitumour drugs.2 The effectiveness of antitumour agents and the other, mostly adverse, biological effects of alkylating agents have been ascribed to their ability to damage cellular macromolecules, in particular DNA. This review concentrates on investigations carried out over the past two years on the role of DNA damage in carcinogenesis, but we shall see how recent advances in this area of research have also led to a better understanding of the mechanisms of the cytotoxic effects of alkylating antitumour agents. (shrink)

The DNA in human cells is continuously undergoing damage as consequences of both endogenous processes and exposure to exogenous agents. The resulting structural changes can be repaired by a number of systems that function to preserve genome integrity. Most pathways are multicomponent, involving incision in the damaged DNA strand and resynthesis using the undamaged strand as a template. In contrast, O6-alkylguanine-DNA alkyltransferase is able to act as a single protein that reverses specific types of alkylation damage simply by removing the (...) offending alkyl group, which becomes covalently attached to the protein and inactivates it. The types of damage that ATase repairs are potentially toxic, mutagenic, recombinogenic and clastogenic. They are generated by certain classes of carcinogenic and chemotherapeutic alkylating agents. There is consequently a great deal of interest in this repair system in relation to both carcinogenesis and cancer chemotherapy. BioEssays 24:255–266, 2002. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/bies.10063. (shrink)

The Dark Side of Technology is aimed at a mass market of intelligent people who are concerned about human progress, interested or amused by many of the unexpected consequences of technological advance, and probably unaware of the dangers which we are accruing for ourselves. Although the book spans a very wide spectrum of ideas, no previous scientific knowledge is required. Other books have focussed on different topic areas, but none have previously presented the generality of the patterns across medicine to (...) agriculture, electronics, communications, a global economy and a burgeoning population. Technology invariably advances faster than our understanding of side effects, or our realisation that we have become vulnerable to natural events that could eliminate advanced nations, nor that mutagenic changes may not be apparent for one or two generations. This is therefore both an alarm call and a guide to survival. (shrink)

In spite of the importance of point mutations for evolution and human diseases, their natural spectrum of incidence in different species is not known. Here I propose to determine these spectra by comparing consecutive sequence periods in stretches of repetitive DNA. The article presents the analysis of more than 51,000 such point mutations identified by this approach in the genomes of human, chimpanzee, rat, mouse, pufferfish, zebrafish, and sea squirt. I propose to explain the observed spectra by auto‐mutagenic mechanisms of (...) genome variation involving the inter‐conversions of nucleotides, single base‐pair inversions and their combinations. (shrink)

In sexual organisms, haploid gametes are produced from diploid germ cells through meiosis. Chromosome reassortment and recombination generate ample genetic variation, augmented by newly arising mutations. Meiotic mutations are associated with recombination, initiated by DNA breakage, and may lead to faster evolution and sequence heterogeneity around recombination hotspots. More details can be found in the Review article 1800235 by Ayelet Arbel‐Eden and Giora Simchen, Elevated Mutagenicity in Meiosis and Its Mechanism, DOI: 10.1002/bies.201970041.

One of the most dynamic areas of plant molecular biology is the investigation of the actions of three classes of herbicides: s‐triazines (atrazine, simazine), glyphosate, and sulfonylureas (chlorsulfuron, sulfometuron methyl) (Figure 1). The results of this work are expected to provide the first significant applications of plant biotechnology: directly, in the genetic engineering of crop plants resistant to specific herbicides and, indirectly, in providing a molecular basis for the rational design of new herbicides for specific biological targets.s‐Triazines affect photosynthesis by (...) inhibiting the binding of quinones to the chloroplast membrane QB protein. An s‐triazine resistant QB protein isolated from weeds in fields consistently treated with the herbicide has a serine in place of a glycine in this highly conserved protein. Glyphosate inhibits 5‐enolpyruvyl‐shikimate‐3‐phosphate synthase (EPSP synthase), an enzyme in the aromatic amino acid biosynthetic pathway. Mutagenized bacteria produce a resistant EPSP synthase with a substitution of serine for proline. Sulfonylureas inhibit the acetolactate synthase (ALS) of bacteria, yeast, and higher plants; this enzyme catalyzes the first step in the synthesis of branched chain amino acids. Resistant ALS has been found in bacteria, yeast and tobacco with a proline substituted by serine in yeast ALS. These findings provide a strong basis for developing projected plant biotechnology applications. (shrink)

The fifth base in human DNA, 5‐methylcytosine, is inherently mutagenic. This has led to marked changes in the distribution of the CpG methyl acceptor site and an 80% depletion in its frequency of occurrence in vertebrate DNA. The coding regions of many genes contain CpGs which are methylated in sperm and serve as hot spots for mutation in human genetic diseases. Fully 30–40% of all human germline point mutations are thought to be methylation induced even though the CpG dinucleotide is (...) under‐represented and efficient cellular repair systems exist. Importantly, tumor suppressor genes such as p53 also contain methylated CpGs and these serve as hot spots for mutations in some, but not all, human cancers. Comparison of the spectrum of mutations present in this gene in different human cancers allows for predictions to be made on the molecular mechanisms of tumorigenesis. (shrink)

There are two ways of preventing induced cellular mutagenesis. In the first, mutagens are inactivated by ‘desmutagens’ before they can attack the DNA. In the second, ‘bio‐antimutagens’ interfere with cellular fixation processes working on damage in DNA. Examples of modes of action are shown for these inhibitors of induced mutations and implications for reducing genetic damage in man are discussed.

The growing number of cloned eukaryotic genes lacking a defined or proven biological function poses a major challenge in ‘reverse genetics’. A method is described here that permits efficient screening for new lesions in, or close to, genes corresponding to cloned DNA sequences of interest. The technique involves transposon mutagenesis, followed by screening of DNA isolated from a population of mutagenised individuals (or their progeny) for evidence that the population contains at least one individual in which transposon insertion has occurred (...) at the target locus. Detection of rare individuals within the population is facilitated by the use of the polymerase chain reaction (PCR). Once recognised, specific individuals (or their progeny) are isolated from the population by a process of sib‐selection. In cases where insertion of the transposon has occurred close to, but not within, the target locus, secondary events involving imprecise excision of the transposon will nonetheless allow the isolation of mutant individuals. Though the method was developed specifically for the transposon‐mutagenesis of Drosophila, extensions to other organisms and to other mutagenic strategies are feasible and some of the possibilities are discussed. (shrink)

On December 18, 2014, a yellow female fly quietly emerged from her pupal case. What made her unique was that she had only one parent carrying a mutant allele of this classic recessive locus. Then, one generation later, after mating with a wild‐type male, all her offspring displayed the same recessive yellow phenotype. Further analysis of other such yellow females revealed that the construct causing the mutation was converting the opposing chromosome with 95% efficiency. These simple results, seen also in (...) mosquitoes and yeast, open the door to a new era of genetics wherein the laws of traditional Mendelian inheritance can be bypassed for a broad variety of purposes. Here, we consider the implications of this fundamentally new form of “active genetics,” its applications for gene drives, reversal and amplification strategies, its potential for contributing to cell and gene therapy strategies, and ethical/biosafety considerations associated with such active genetic elements. (shrink)

This chapter contains section titled: Introduction General Scenario for the Transmission of Information and Its Application to Genetics Semiotic Dimensions of Biological Information Syntactic Dimension I: Measuring the Statistical Entropy of Signals and Messages Syntactic Dimension II: Estimating the Algorithmic Complexity of Signals and Messages Semantic Dimension: Classifying the Mutual Complexity of Transmitters and Receivers Acknowledgment References Further Reading.