Error-prone DNA polymerase specifically involved in DNA repair (PubMed:15026325, PubMed:16357261). Plays an important role in translesion synthesis, where the normal high-fidelity DNA polymerases cannot proceed and DNA synthesis stalls (PubMed:15026325, PubMed:16357261). Favors Hoogsteen base-pairing in the active site. Inserts the correct base with high-fidelity opposite an adenosine template (By similarity). Exhibits low fidelity and efficiency opposite a thymidine template, where it will preferentially insert guanosine (By similarity). May play a role in hypermutation of immunoglobulin genes (By similarity). Forms a Schiff base with 5'-deoxyribose phosphate at abasic sites, but may not have lyase activity (By similarity). a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Binds nucleotide much more tightly and catalyzes nucleotide insertion much more efficiently in the presence of Mg(2+) than in the presence of Mn(2+). Interacts with POLH (By similarity). Interacts with REV1 (PubMed:14657033). Interacts with ubiquitin (PubMed:16357261). Binding to ubiquitin mediates localization to replication forks after UV-induced DNA damage. Detected in testis, and at very low levels in spleen, lung and brain. Detected in round spermatids, but not in prophase spermatocytes. The catalytic core consists of fingers, palm and thumb subdomains, but the fingers and thumb subdomains are much smaller than in high-fidelity polymerases; residues from five sequence motifs of the Y-family cluster around an active site cleft that can accommodate DNA and nucleotide substrates with relaxed geometric constraints, with consequently higher rates of misincorporation and low processivity. Ubiquitin-binding motif 1 and ubiquitin-binding motif 2 regulate POLI protein monoubiquitination and localization to nuclear foci after UV-induced DNA damage. Monoubiquitinated (PubMed:16357261). Protein monoubiquitination prevents POLI binding to ubiquitin via the ubiquitin-binding motif 1 and ubiquitin-binding motif 2 (PubMed:16357261). Belongs to the DNA polymerase type-Y family.