As part of the heterotrimeric replication protein A complex (RPA/RP-A), binds and stabilizes single-stranded DNA intermediates, that form during DNA replication or upon DNA stress. It prevents their reannealing and in parallel, recruits and activates different proteins and complexes involved in DNA metabolism (PubMed:27723720, PubMed:27723717). Thereby, it plays an essential role both in DNA replication and the cellular response to DNA damage (PubMed:9430682). In the cellular response to DNA damage, the RPA complex controls DNA repair and DNA damage checkpoint activation. Through recruitment of ATRIP activates the ATR kinase a master regulator of the DNA damage response (PubMed:24332808). It is required for the recruitment of the DNA double-strand break repair factors RAD51 and RAD52 to chromatin in response to DNA damage (PubMed:17765923). Also recruits to sites of DNA damage proteins like XPA and XPG that are involved in nucleotide excision repair and is required for this mechanism of DNA repair (PubMed:7697716). Also plays a role in base excision repair (BER) probably through interaction with UNG (PubMed:9765279). Also recruits SMARCAL1/HARP, which is involved in replication fork restart, to sites of DNA damage. May also play a role in telomere maintenance (PubMed:17959650). As part of the alternative replication protein A complex, aRPA, binds single-stranded DNA and probably plays a role in DNA repair. Compared to the RPA2-containing, canonical RPA complex, may not support chromosomal DNA replication and cell cycle progression through S-phase. The aRPA may not promote efficient priming by DNA polymerase alpha but could support DNA synthesis by polymerase delta in presence of PCNA and replication factor C (RFC), the dual incision/excision reaction of nucleotide excision repair and RAD51-dependent strand exchange (PubMed:19996105). Component of the canonical replication protein A complex (RPA), a heterotrimer composed of RPA1, RPA2 and RPA3 (PubMed:27723720, PubMed:27723717). Also a component of the aRPA, the alternative replication protein A complex, a trimeric complex similar to the replication protein A complex/RPA but where RPA1 and RPA3 are associated with RPA4 instead of RPA2 (PubMed:7760808, PubMed:19116208). The DNA-binding activity may reside exclusively on the RPA1 subunit. Interacts with PRPF19; the PRP19-CDC5L complex is recruited to the sites of DNA repair where it ubiquitinates the replication protein A complex (RPA) (PubMed:24332808). Interacts with RIPK1 (PubMed:16135809). Interacts with the polymerase alpha subunit POLA1/p180; this interaction stabilizes the replicative complex and reduces the misincorporation rate of DNA polymerase alpha by acting as a fidelity clamp (PubMed:9214288). Interacts with RAD51 and SENP6 to regulate DNA repair (PubMed:20705237). Interacts with HELB; this interaction promotes HELB recruitment to chromatin following DNA damage (PubMed:22194613, PubMed:26774285). Interacts with PRIMPOL; leading to recruit PRIMPOL on chromatin and stimulate its DNA primase activity (PubMed:24126761, PubMed:25550423, PubMed:28534480). Interacts with XPA; the interaction is direct and associates XPA with the RPA complex (PubMed:7700386, PubMed:9699634, PubMed:10563794). Interacts with ETAA1; the interaction is direct and promotes ETAA1 recruitment at stalled replication forks (PubMed:27601467, PubMed:27723720, PubMed:27723717). Interacts with RPA1; this interaction associates HROB with the RPA complex (By similarity). Enriched in PML bodies in cells displaying alternative lengthening of their telomeres. DNA damage-induced 'Lys-63'-linked polyubiquitination by PRPF19 mediates ATRIP recruitment to the RPA complex at sites of DNA damage and activation of ATR (PubMed:24332808). Ubiquitinated by RFWD3 at stalled replication forks in response to DNA damage: ubiquitination by RFWD3 does not lead to degradation by the proteasome and promotes removal of the RPA complex from stalled replication forks, promoting homologous recombination (PubMed:26474068). Sumoylated on lysine residues Lys-449 and Lys-577, with Lys-449 being the major site. Sumoylation promotes recruitment of RAD51 to the DNA damage foci to initiate DNA repair through homologous recombination. Desumoylated by SENP6. Belongs to the replication factor A protein 1 family. Extended N-terminus.