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Nature. 2006 Feb 2;439(7076):557-62.

Replication fork reactivation downstream of a blocked nascent leading strand.

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Molecular Biology Program, Weill Graduate School of Medical Sciences of Cornell University, New York, New York 10021, USA.


Unrepaired lesions in the DNA template pose a threat to accurate replication. Several pathways exist in Escherichia coli to reactivate a blocked replication fork. The process of recombination-dependent restart of broken forks is well understood, but the consequence of replication through strand-specific lesions is less well known. Here we show that replication can be restarted and leading-strand synthesis re-initiated downstream of an unrepaired block to leading-strand progression, even when the 3'-OH of the nascent leading strand is unavailable. We demonstrate that the loading by a replication restart system of a single hexamer of the replication fork helicase, DnaB, on the lagging-strand template is sufficient to coordinate priming by the DnaG primase of both the leading and lagging strands. These observations provide a mechanism for damage bypass during fork reactivation, demonstrate how daughter-strand gaps are generated opposite leading-strand lesions during the replication of ultraviolet-light-irradiated DNA, and help to explain the remarkable speed at which even a heavily damaged DNA template is replicated.

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