Replication stress response protein that accumulates at DNA damage sites and promotes replication fork progression and integrity (PubMed:27601467, PubMed:27723720, PubMed:27723717). Recruited to stalled replication forks via interaction with the RPA complex and directly stimulates ATR kinase activity independently of TOPBP1 (PubMed:27723720, PubMed:27723717). Probably only regulates a subset of ATR targets (PubMed:27723720, PubMed:27723717). Interacts (via RBM1 motif) with RPA1 (PubMed:27601467, PubMed:27723720, PubMed:27723717). Interacts (via RBM2 motif) with RPA2 (PubMed:27601467, PubMed:27723720, PubMed:27723717). Interacts (via the ATR-activation domain motif) with ATR (PubMed:27723720, PubMed:27723717). Localizes at sites of DNA damage following replication stress (PubMed:27601467, PubMed:27723720, PubMed:27723717). Recruited to stalled replication forks via interaction with RPA1 and RPA2 subunits of the RPA complex (PubMed:27601467, PubMed:27723720). Expressed at high levels in the brain, liver kidney and Ewing tumor cell lines. The RBM1 (RPA1-binding, also named RPA70N-binding) motif mediates interaction with RPA1 (PubMed:27601467, PubMed:27723720, PubMed:27723717). The RBM2 (RPA2-binding, also named RPA32C-binding) motif mediates interaction with RPA2 (PubMed:27601467, PubMed:27723720, PubMed:27723717). The ATR-activation domain (AAD) motif is required to bind and activate ATR (PubMed:27723720, PubMed:27723717). Phosphorylated by ATR. Initially reported to localize in the cytoplasm (PubMed:16003559). A number of studies showed that it accumulates at DNA damage sites in the nucleus (PubMed:27601467, PubMed:27723720, PubMed:27723717).