title: PCNA trimer instability inhibits translesion synthesis by DNA polymerase η and by DNA polymerase δ.
abstract: Translesion synthesis (TLS), the process by which DNA polymerases replicate through DNA lesions, is the source of most DNA damage-induced mutations. Sometimes TLS is carried out by replicative polymerases that have evolved to synthesize DNA on non-damaged templates. Most of the time, however, TLS is carried out by specialized translesion polymerases that have evolved to synthesize DNA on damaged templates. TLS requires the mono-ubiquitylation of the replication accessory factor proliferating cell nuclear antigen (PCNA). PCNA and ubiquitin-modified PCNA (UbPCNA) stimulate TLS by replicative and translesion polymerases. Two mutant forms of PCNA, one with an E113G substitution and one with a G178S substitution, support normal cell growth but inhibit TLS thereby reducing mutagenesis in yeast. A re-examination of the structures of both mutant PCNA proteins revealed substantial disruptions of the subunit interface that forms the PCNA trimer. Both mutant proteins have reduced trimer stability with the G178S substitution causing a more severe defect. The mutant forms of PCNA and UbPCNA do not stimulate TLS of an abasic site by either replicative Pol δ or translesion Pol η. Normal replication by Pol η was also impacted, but normal replication by Pol δ was much less affected. These findings support a model in which reduced trimer stability causes these mutant PCNA proteins to occasionally undergo conformational changes that compromise their ability to stimulate TLS by both replicative and translesion polymerases.
authors.affiliation: Department of Biochemistry, University of Iowa College of Medicine, Iowa City, IA 52242-1109, United States.
authors.forename: Lynne M
authors.initials: LM
authors.lastname: Dieckman
authors.forename: M Todd
authors.initials: MT
authors.lastname: Washington
mesh_terms: D001665:Binding Sites; D004258:DNA Polymerase III / Q000378:metabolism*; D004260:DNA Repair; D004261:DNA Replication; D004271:DNA, Fungal / Q000378:metabolism*; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D059645:Mutation Rate; D020125:Mutation, Missense; D018809:Proliferating Cell Nuclear Antigen / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D055550:Protein Stability; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination; D000099270:Y-Family DNA Polymerases
chemical_list: D004258:DNA Polymerase III; D004271:DNA, Fungal; D004259:DNA-Directed DNA Polymerase; D018809:Proliferating Cell Nuclear Antigen; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; C112338:Rad30 protein; D000099270:Y-Family DNA Polymerases