PerspectiveDNA REPLICATION

Terminating the replisome

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Science  24 Oct 2014:
Vol. 346, Issue 6208, pp. 418-419
DOI: 10.1126/science.1261245

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Summary

In a eukaryotic cell, DNA replication begins with the unwinding of double-stranded DNA at an origin, followed by the synthesis of complementary strands that grow bidirectionally along the original DNA strands (forming a replication fork) from the origin. This synthesis is carried out by a complex structure called a replisome, the heart of which is a ring-shaped DNA helicase that unwinds the DNA. Two key events occur when replication forks arising from two different origins converge. The DNA associated with each fork first must be fully replicated and separated from each other; topoisomerases facilitate both fork convergence and this decatenation (13). Then, the replisome associated with each converging fork must be dismantled. Because the DNA helicase cannot be reloaded onto DNA once it is removed, the processivity of replication demands that these enzymes associate tightly with substrate DNA. On pages 440 and 477 of this issue, Maric et al. (4) and Priego Moreno et al. (5), respectively, demonstrate that disassembly of the eukaryotic replicative DNA helicase is actively controlled.