The function of REV1 (REV1 DNA directed polymerase, ENSG00000135945) is as follows. Bifunctional protein involved in the maintenance of genome stability through translesion DNA synthesis (TLS) and antibody diversification via somatic hypermutation (PubMed:16263170, PubMed:23143872). Functions as a molecular adapter protein at stalled DNA replication, coordinating polymerases recruitment, selection, and switching, in a manner independent of its deoxycytidyl transferase activity (PubMed:23143872). At the site of DNA lesion, recruits and mediates the switch between low-fidelity inserter DNA polymerases, such as POLK, that incorporate nucleotides opposite lesions and the extender DNA polymerase zeta complex which continues DNA synthesis from distorted primer termini (PubMed:23143872). In vitro, acts as a template-dependent deoxycytidyl transferase that preferentially incorporates deoxycytidine residues from dCTP to the 3'-end of a DNA primer opposite apurinic/apyrimidinic (AP) site, uracil, undamaged DNA templates (G > A > C > T) and a variety of damaged DNA templates (PubMed:10536157, PubMed:11278384, PubMed:38612916). Opposite template guanine, efficiently incorporates not only dCMP but also non- complementary dGMP and dTMP, with lower efficiency for dAMP, demonstrating low fidelity on undamaged DNA (PubMed:10536157, PubMed:11711549, PubMed:38612916). This catalytic activity has been implicated in somatic hypermutation, likely achieved by incorporation of deoxycytidine opposite abasic sites, generated at cytidines via activation-induced deoxycytidine deaminase (AID)-mediated deamination and uracil DNA glycosylase (UNG) activity, respectively (PubMed:16263170). In addition, exhibits a 5'-deoxyribose-5-phosphate lyase activity in vitro, though its necessity in vivo is not confirmed (By similarity). {ECO:0000250|UniProtKB:Q920Q2, ECO:0000269|PubMed:10536157, ECO:0000269|PubMed:11278384, ECO:0000269|PubMed:11711549, ECO:0000269|PubMed:16263170, ECO:0000269|PubMed:23143872, ECO:0000269|PubMed:38612916}.