In vivo reconstitution of Saccharomyces cerevisiae DNA polymerase ε in insect cells -: Purification and characterization

DNA polymerase epsilon (pot epsilon) is a multiple subunit complex consisting of at least four proteins, including catalytic Po12p, Dpb2p, Dpb3p, and Dpb4p. Pot epsilon has been shown to play essential roles in chromosomal DNA replication. Here, we report reconstitution of the yeast pol epsilon complex, which was expressed and purified from baculovirus-infected insect cells. During the purification, we were able to resolve the pol epsilon complex and truncated Po12p (140 kDa), as was observed initially with the pot epsilon purified from yeast. Biochemical characterization of subunit stoichiometry, salt sensitivity, processivity, and stimulation by proliferating cell nuclear antigen indicates that the reconstituted pot epsilon is functionally identical to native pot epsilon purified from yeast and is therefore useful for biochemical characterization of the interactions of pol epsilon with other replication, recombination, and repair proteins. Identification and characterization of a proliferating cell nuclear antigen consensus interaction domain on Po12p indicates that the motif is dispensable for DNA replication but is important for methyl methanesulfonate damage-induced DNA repair. Analysis of the putative zinc finger domain of Po12p for zinc binding capacity demonstrates that it binds zinc. Mutations of the conserved cysteines in the putative zinc finger domain reduced zinc binding, indicating that cysteine ligands are directly involved in binding zinc.