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. Author manuscript; available in PMC: 2013 May 8.
Published in final edited form as: Nat Struct Mol Biol. 2011 Jul 6;18(7):748–754. doi: 10.1038/nsmb.2096

Figure 1. DNA repair by HR.

Figure 1

Schematics are shown illustrating how repair of DNA with a DSB or ssDNA gap could initiate by HR. Both pathways begin with invasion of a ssDNA tract (step i or i-a) into a homologous DNA sequence. In DSB repair the D-loop formed after invasion of the ssDNA tail (step ii) is extended by DNA synthesis (step iii) until it can pair with, or capture, the second end through exposed complementary sequence. The 3′ strand of the second end serves as a primer for fill-in synthesis (step iv). Additional processing of the intermediates and several subsequent steps results in a repaired chromosome. In the other pathway, termed post-replication repair, a ssDNA gap generated during DNA replication of a damaged template (step i-a) invades the undamaged homologous sequence present in the sister chromatid (step ii-a). By branch migration through a short tract the 3′ end of the broken strand switches templates (step iii-a) and then serves as primer for fill-in synthesis (step iv-a). After additional steps the intermediate is resolved and repair is completed.