The 9-1-1 checkpoint clamp physically interacts with Pol zeta and is partially required for spontaneous Pol zeta-dependent mutagenesis in Saccharomyces cerevisiae

The use of translesion synthesis (TLS) polymerases to bypass DNA lesions during replication constitutes an important mechanism to restart blocked/stalled DNA replication forks. Because TLS polymerases generally have low fidelity on undamaged DNA, the cell must regulate the interaction of TLS polymerases with damaged versus undamaged DNA to maintain genome integrity. The Saccharomyces cerevisiae checkpoint proteins Ddc1, Rad17, and Mec3 form a clamp-like structure (the 9-1-1 clamp) that has physical similarity to the homotrimeric sliding clamp proliferating cell nuclear antigen, which interacts with and promotes the processivity of the replicative DNA polymerases. In this work, we demonstrate both an in vivo and in vitro physical interaction between the Mec3 and Ddc1 subunits of the 9-1-1 clamp and the Rev7 subunit of the Pol zeta TLS polymerase. In addition, we demonstrate that loss of Mec3, Ddc1, or Rad17 results in a decrease in Pol zeta-dependent spontaneous mutagenesis. These results suggest that, in addition to its checkpoint signaling role, the 9-1-1 clamp may physically regulate Pol zeta-dependent mutagenesis by controlling the access of Pol zeta to damaged DNA.