背景 |
One factor that plays essential roles both during DNA replication and in the repair- and recombination-mediated recovery from damage is replication protein A (RPA), the eukaryotic single-stranded (ss) DNA-binding protein. RPA is a heterotrimeric protein consisting, in mammalian cells, of ∼70- (RPA1), 30- (RPA2), and 14 (RPA3)-kDa subunits. During DNA replication, RPA acts at the fork, stabilizing ssDNA and facilitating nascent strand synthesis by the replicative DNA polymerases. Under DNA-damaging conditions, RPA-ssDNA complexes act to recruit and activate a key checkpoint mediator consisting of the ATR and ATRIP (ATR-interacting protein) protein-kinase complex. At DNA damage-dependent nuclear foci, RPA interacts with repair and recombination components to process double-strand DNA breaks and other lesions. RPA activity is regulated by various stress conditions. In particular, heat shock, exposure to UV radiation, and treatment with DNA-alkylating agents each cause the generation of an RPA species that is unable to support DNA replication in vitro. Two of the RPA2 sites (S23 and S29) are phosphorylated in a cell cycle-dependent manner by cyclin-cdk2 complexes. At least five of the other seven (S4, S8, S11, S12, S13, T21, and S33) can be phosphorylated in response to UV irradiation. |