Bass KL, Murray JM, O'Connell MJ

Brc1 is a multi-BRCT domain protein in Schizosaccharomyces pombe that is required for resistance to chronic replicative stress, but whether this reflects a repair or replication defect is unknown and the subject of this study. Rad52 is a homologous recombination protein that loads the Rad51 recombinase at resected dsDNA breaks ...

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and is also recruited to stalled replication forks, where it may stabilize structures through its strand annealing activity. We show that brc1Δ cells are significantly delayed in recovery from replication pausing, though this does not activate a DNA damage checkpoint. Rad52 is required for the viability of brc1Δ cells, and brc1Δ cells accumulate Rad52 foci late in S-phase that are potentiated by replication stress. However, these foci contain the ssDNA binding protein RPA, but not Rad51 or γH2A. Further, these foci are not associated with increased recombination between repeated sequences, nor increased post-replication repair. Thus, these Rad52 foci do not represent sites of recombination. Following the initiation of DNA replication, the induction of these foci by replication stress is suppressed by defects in ORC function, which is accompanied by loss of viability and severe mitotic defects. This suggests that cells lacking Brc1 undergo an ORC-dependent rescue of replication stress, presumably through the firing of dormant origins, and this generates RPA-coated ssDNA and recruits Rad52. However, as Rad51 is not recruited, and Chk1 is not activated, these structures must not contain the unprotected primer ends found at sites of DNA damage that are required for recombination and checkpoint activation.

Date: Feb. 24, 2012

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