Defect of Dpb2p, a noncatalytic subunit of DNA polymerase ɛ, promotes error prone replication of undamaged chromosomal DNA in Saccharomyces cerevisiae.

The Saccharomyces cerevisiae DNA polymerase epsilon holoenzyme (Pol ɛ HE) is composed of four subunits: Pol2p, Dpb2p, Dpb3p and Dpb4p. The biological functions of Pol2p, the catalytic subunit of Pol ɛ, are subject of active investigation, while the role of the other three, noncatalytic subunits, is not well defined. We showed previously that mutations in Dpb2p, a noncatalytic but essential subunit of Pol ɛ HE, influence the fidelity of DNA replication in yeast cells. The strength of the mutator phenotype due to the different dpb2 alleles was inversely proportional to the strength of protein-protein interactions between Pol2p and the mutated forms of Dpb2p. To understand better the mechanisms of the contribution of Dpb2p to the controlling of the level of spontaneous mutagenesis we undertook here a further genetic analysis of the mutator phenotype observed in dpb2 mutants. We demonstrate that the presence of mutated forms of Dpb2p in the cell not only influences the intrinsic fidelity of Pol ɛ but also facilitates more frequent participation of error-prone DNA polymerase zeta (Pol ζ) in DNA replication. The obtained results suggest that the structural integrity of Pol ɛ HE is a crucial contributor to accurate chromosomal DNA replication and, when compromised, favors participation of error prone DNA Pol ζ in this process.