Pph3 Phosphatase Participates in the Regulation of the Error-Free Branch of Postreplication DNA Repair in Yeast Saccharomyces cerevisiae

The phosphatase complex PPH3 consists of three subunits: catalytic Pph3 and auxiliary Pph2 and Psy4. Pph3 also forms a double complex with subunit Psy2, which binds to kinase Rad53 and dephosphorylates it without recruiting the third subunit. The triple complex dephosphorylates γH2A. We have previously shown that gene HSM6 corresponds to gene PSY4 on the genetic map of Saccharomyces cerevisiae . Mutation hsm6-1 increases the rate of spontaneous and UV-induced mutagenesis. In this work, we have shown that mutations in gene PPH3 increase the rate of spontaneous reparative mutagenesis sevenfold, while mutations pph3 Δ and hsm6-1 show an epistatic effect. At high doses, the frequency of UV-induced mutations in mutants pph3 Δ, psy4 Δ, and hsm6-1 is the same and exceeds the level of mutagenesis in the wild-type strain by approximately twofold. All mutants show a higher (approximately 10-fold) frequency of γ-induced mutations compared to the wild-type strain. The combination of mutations in genes encoding PPH3 subunits and mutations in MMS2 and XRS2 , which control an error-free postreplication repair pathway, leads to blocking of PPH3-specific UV-induced mutagenesis. Thus, we have identified the PPH3 complex as a novel factor involved in the regulation of the error-free branch of postreplication repair. The double mutant for genes PTC2 and PTC3 , encoding the other two phosphatases that dephosphorylate Rad53, does not differ from the wild-type strain with respect to UV-induced mutagenesis and survival. This means that hyperphosphorylation of only the Pph3-specific sites of protein Rad53 and histone H2A increases the level of UV mutagenesis.