Pol32 is required for Polζ-dependent translesion synthesis and prevents double-strand breaks at the replication fork

POL32 encodes a non-essential subunit of Pol delta and plays a role in Pol delta processivity and DNA repair. In order to understand how Pol32 is involved in these processes, we performed extensive genetic analysis and demonstrated that POL32 is required for Pol zeta-mediated translesion synthesis, but not for Pol eta-mediated activity. Unlike Pol zeta, inactivation of Pol32 does not result in decreased spontaneous mutagenesis, nor does it limit genome instability in the absence of the error-free postreplication repair pathway. In contrast, inactivation of Po132 results in an increased rate of replication slippage and recombination. A genome-wide synthetic lethal screen revealed that in the absence of Po132, homologous recombination repair and cell cycle checkpoints play crucial roles in maintaining cell survival and growth. These results are consistent with a model in which Po132 functions as a coupling factor to facilitate a switch from replication to translesion synthesis when Pol delta encounters replication-blocking lesions. When Po132 is absent, the S-phase checkpoint complex Mrc1-Tof1 becomes crucial to stabilize the stalled replication fork and recruit Top3 and Sgs1. Lack of any of the above activities will cause double strand breaks at or near the replication fork that require recombination as well as Rad9 for cell survival. (c) 2007 Elsevier B.V. All rights reserved.