Regulation of translesion synthesis DNA polymerase by η monoubiquitination

DNA polymerase η is a Y-family polymerase involved in translesion synthesis (TLS). Its action is initiated by simultaneous interaction between the PIP box in polη and PCNA, and between the UBZ in polη and monoubiquitin attached to PCNA. While monoubiquitination of PCNA is required for its interaction with polη during TLS, we now show that monoubiquitination of polη inhibits this interaction, preventing its functions in undamaged cells. Identification of monoubiquitination sites within polη nuclear localization signal (NLS) led to the discovery that polη NLS directly contacts PCNA, forming an extended polη-PCNA interaction surface. We name this region PIR (PCNA-Interacting Region) and show that its monoubiquitination is downregulated by various DNA-damaging agents. We propose that this mechanism ensures optimal availability of non-ubiquitinated, TLS-competent polη after DNA damage. Our work shows how monoubiquitination can either positively or negatively regulate the assembly of a protein complex depending on which substrates are targeted by ubiquitin. Suggested Reviewers: