As part of the replication protein A (RPA/RP-A), a single-stranded DNA-binding heterotrimeric complex, may play an essential role in DNA replication, recombination and repair. Binds and stabilizes single-stranded DNA intermediates, preventing complementary DNA reannealing and recruiting different proteins involved in DNA metabolism. Binds to single-stranded sequences participating in DNA replication in addition to those mediating transcriptional repression (URS1) and activation (CAR1). Stimulates the activity of a cognate strand exchange protein (SEP1). It cooperates with T-AG and DNA topoisomerase I to unwind template DNA containing the simian virus 40 origin of DNA replication. Component of the heterotrimeric canonical replication protein A complex (RPA). Interacts with POB3. The N-terminus is blocked. Present with 4100 molecules/cell in log phase SD medium. Belongs to the replication factor A protein 1 family.