Has an imporant role in DNA replication and in maintaining genome integrity during replication stress. Involved in a RAD9A-related damage checkpoint, a pathway that is important in determining whether DNA damage is compatible with cell survival or whether it requires cell elimination by apoptosis. Modulates the RAD9A interaction with BCL2 and thereby induces DNA damage-induced apoptosis (PubMed:15983387). Promotes PCNA deubiquitination by recruiting the ubiquitin-specific protease 1 (USP1) and WDR48 thereby down-regulating the error-prone damage bypass pathway. As component of the ATAD5 RFC-like complex, regulates the function of the DNA polymerase processivity factor PCNA by unloading the ring-shaped PCNA homotrimer from DNA after replication during the S phase of the cell cycle. This seems to be dependent on its ATPase activity. Plays important roles in restarting stalled replication forks under replication stress, by unloading the PCNA homotrimer from DNA and recruiting RAD51 possibly through an ATR-dependent manner. Ultimately this enables replication fork regression, breakage, and eventual fork restart. Both the PCNA unloading activity and the interaction with WDR48 are required to efficiently recruit RAD51 to stalled replication forks. Promotes the generation of MUS81-mediated single-stranded DNA-associated breaks in response to replication stress, which is an alternative pathway to restart stalled/regressed replication forks (By similarity). Component of a heteropentameric replication factor ATAD5 RFC-like complex composed of one large subunit (ATAD5) and four small subunits (RFC2, RFC3, RFC4 and RFC5). Within the ATAD5 RFC-like complex, interacts with RFC2, RFC4 and RFC5. Within the ATAD5 RFC-like complex, interacts directly via-N terminal with RAD51; the interactions is enhanced under replication stress (By similarity). Interacts with RB1 predominantly in G1 phase via its LXCXE motif (PubMed:15983387). Interacts with RAD9A in growing cells (PubMed:15983387). The interaction with RAD9A is reduced after exposure to DNA replication-inhibiting agents (PubMed:15983387). Interacts with BRD4. Interacts with PCNA. Interacts with deubiquitinating enzyme USP1, and its associated factor, WDR48 (By similarity). Accumulates in nuclear foci at sites of stalled DNA replication forks in response to DNA damage. Expressed ubiquitously in all cell lines like teratocarcinoma, cell lymphoma, lymphoma. Down-regulated by DNA replication-inhibiting agents. ATR may stimulate the RAD9A dissociation. Belongs to the AAA ATPase family. Contaminating sequence. Potential poly-A sequence.