Catalytic subunit of the DNA polymerase zeta complex, an error-prone polymerase specialized in translesion DNA synthesis (TLS). Lacks an intrinsic 3'-5' exonuclease activity and thus has no proofreading function. a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Binds 1 [4Fe-4S] cluster. Heterodimer with MAD2L2. This dimer forms the minimal DNA polymerase zeta complex (Pol-zeta2), with REV3L bearing DNA polymerase catalytic activity, although its activity is very low in this context. Component of the tetrameric Pol-zeta complex (Pol-zeta4), which consists of REV3L, MAD2L2, POLD2 and POLD3; Pol-zeta4 is the fully active form of DNA polymerase zeta. The CysB motif binds 1 4Fe-4S cluster and is required for the formation of polymerase complexes. Belongs to the DNA polymerase type-B family.