Abstract

The process by which the genetically identical cell lineages of a multicellular organism acquire the propensity to express distinct arrays of gene products is among the most significant and fascinating questions in modern biology. Not surprisingly, this complex process requires control at several levels, each level providing a condition that is necessary but not sufficient for transcription to occur. Evidence suggests that one level of control concerns a region of DNA much larger than the transcription unit itself – the chromatin domain. This domain must be in a specific chromatin conformation in order to permit transcription; other control mechanisms may be required to bring about overt transcription. A hypothesis concerning the nature of chromatin domains and the relationship between early replication and transcription potential is presented.