Catalytic subunit of the error prone DNA polymerase zeta. Involved in damage-tolerance mechanisms through translesion DNA synthesis. a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) Binds 1 [4Fe-4S] cluster. Forms DNA polymerase zeta with REV7. A number of isoforms are produced. According to EST sequences. Expressed in roots, leaves and flowers. The CysB motif binds 1 4Fe-4S cluster and is required for the formation of polymerase complexes. No visible phenotype under normal growth conditions, but mutant plants are hypersensitive to UV-B light and gamma rays. Belongs to the DNA polymerase type-B family.