Knot what we thought before: the twisted story of replication

Article Abstract:

Author's Abstract: COPYRIGHT 1999, John Wiley & Sons, Inc 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 onlymethod of unlinking the parental strands. Recent evidence implies that supercoils candiffuse 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.

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The structure of supercoiled intermediates in DNA replication

Article Abstract:

Superhelical stress is distributed throughout the whole partially replicated molecule in intermediates produced both in vitro with purified components and in vivo. The unreplicated region is supercoiled, and daughter DNA segments are wound around each other. This finding changes the traditional view of replication intermediates and the roles of topoisomerases in replication. If the (+)delta-Lk does not equilibrate in vivo, there must be an active mechanism for sequestering delta-Lk in unreplicated DNA.

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Topological domain structure of the Escherichia coli chromosome

Article Abstract:

The organization of the circular chromosome of Escherichia coli into independently supercoiled loops, or topological domains, and its size are examined in vivo and vitro. The results are compared to Monte Carlo simulations of domain organization models, and it is concluded that domain barriers are not placed at fixed sites on the chromosome but instead are effectively randomly distributed.

Science & research, Research, Escherichia coli, Simulation methods, Simulation, Genetic research, Monte Carlo method, Monte Carlo methods, Structure

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