Just as the faithful replication of DNA is an essential process for the cell, chromatin structures of active and inactive genes have to be copied accurately. Under certain circumstances, however, the activity pattern has to be changed in specific ways. Although analysis of specific aspects of these complex processes, by means of model systems, has led to their further elucidation, the mechanisms of chromatin replication in vivo are still controversial and far from being understood completely. Progress has been achieved in (...) understanding: 1. The initiation of chromatin replication, indicating that a nucleosome‐free origin is necessary for the initiation of replication; 2. The segregation of the parental nucleosomes, where convincing data support the model of random distribution of the parental nucleosomes to the daughter strands; and 3. The assembly of histones on the newly synthesized strands, where growing evidence is emerging for a two‐step mechanism of nucleosome assembly, starting with the deposition of H3/H4 tetramers onto the DNA, followed by H2A/H2B dimers. (shrink)

I consider a situation in which workers have present-biased preferences and tend to procrastinate their tasks, but underestimate the degree of self-control problems that they will face in the future. Brocas and Carrillo show that a form of competition always mitigates delay in a setting where agents are perfectly aware of their future self-control problems. However, I show that the introduction of the competition considered in their paper does not necessarily mitigate delay in a setting where agents underestimate the magnitude (...) of their future self-control problems. The intuition is that competition reinforces their belief that they will complete earlier, which undermines their incentive to complete now. This result holds even when there is only one worker who severely underestimates the degree of his or her future self-control problem, suggesting that the mere existence of a single “irrational” agent can undermine the overall performance of organizations. Moreover, the intuition behind my result implies that, to mitigate procrastination, it is important to design schemes in which workers believe that they will not complete early in the future, e.g., reducing competition over time, increasing cost over time, or even enforcing no work day tomorrow. (shrink)

DNA replication requires the unwinding of the parental duplex, which generates (+) supercoiling ahead of the replication fork. It has been thought that removal of these (+) supercoils was the only method of unlinking the parental strands. Recent evidence implies that supercoils can diffuse across the replication fork, resulting in interwound replicated strands called precatenanes. Topoisomerases can then act both in front of and behind the replication fork. A new study by Sogo et al. [J Mol Biol 1999;286:637–643 (Ref. (...) 1)], using a topological analysis, provides the best evidence that precatenanes exist in negatively supercoiled, partially replicated molecules in vivo. BioEssays 21:805–808, 1999. © 1999 John Wiley & Sons, Inc. (shrink)

DNA replication requires the unwinding of the parental duplex, which generates (+) supercoiling ahead of the replication fork. It has been thought that removal of these (+) supercoils was the only method of unlinking the parental strands. Recent evidence implies that supercoils can diffuse across the replication fork, resulting in interwound replicated strands called precatenanes. Topoisomerases can then act both in front of and behind the replication fork. A new study by Sogo et al. [J Mol Biol 1999;286:637–643 (Ref. (...) 1)], using a topological analysis, provides the best evidence that precatenanes exist in negatively supercoiled, partially replicated molecules in vivo. BioEssays 21:805–808, 1999. © 1999 John Wiley & Sons, Inc. (shrink)