Human Ctf18-RFC, a PCNA loader complex, interacts with DNA polymerase å (Polå) through a structure formed by the Ctf18, Dcc1 and Ctf8 subunits. The C-terminal stretch of Ctf18, which is highly conserved from yeast to human, is necessary to form the Polå-capturing structure. We found that in the budding yeast Saccharomyces cerevisiae, Ctf18, Dcc1 and Ctf8 formed the same structure through the conserved C-terminus and interacted specifically with Polå. Thus, the specific interaction of Ctf18-RFC with Polå is a conserved feature between these proteins. A C-terminal deletion mutant of Ctf18 (ctf18(ÄC) ) exhibited the same high sensitivity to hydroxyurea as the complete deletion strain (ctf18Ä) or ATPase-deficient mutant (ctf18(K189A) ), but was somewhat less sensitive to methyl methanesulfonate than either of them. These phenotypes were also observed in dcc1Ä and ctf8Ä, predicted to be deficient in the interaction with Polå. Furthermore, both plasmid loss and gross chromosomal rearrangement (GCR) rates were increased in ctf18(ÄC) cells to the same extent as in ctf18Ä cells. These results indicate that the Ctf18-RFC/Polå interaction plays a crucial role in maintaining genome stability in budding yeast, probably through recruitment of this PCNA loader to the replication fork.
Animals Chromosomal Proteins, Non-Histone