BRCA1 promotes the ubiquitination of PCNA and recruitment of translesion polymerases in response to replication blockade.

Breast cancer gene 1 (BRCA1) deficient cells not only are hypersensitive to double-strand breaks but also are hypersensitive to UV irradiation and other agents that cause replication blockade; however, the molecular mechanisms behind these latter sensitivities are largely unknown. Here, we report that BRCA1 promotes cell survival by directly regulating the DNA damage tolerance pathway in response to agents that create cross-links in DNA. We show that BRCA1 not only promotes efficient mono- and polyubiquitination of proliferating cell nuclear antigen (PCNA) by regulating the recruitment of replication protein A, Rad18, and helicase-like transcription factor to chromatin but also directly recruits translesion polymerases, such as Polymerase eta and Rev1, to the lesions through protein-protein interactions. Our data suggest that BRCA1 plays a critical role in promoting translesion DNA synthesis as well as DNA template switching.