title: Evidence that MutY and MutM combine to prevent mutations by an oxidatively damaged form of guanine in DNA.
abstract: It has been previously shown both in vivo and in vitro that DNA synthesis past an oxidatively damaged form of guanine, 7,8-dihydro-8-oxoguanine (8-oxoG), can result in the misincorporation of adenine (A) opposite the 8-oxodG. In this study we show that MutY glycosylase is active on a site-specific, oxidatively damaged A/8-oxoG mispair and that it removes the undamaged adenine from this mispair. Strains that lack active MutY protein have elevated rates of G.C----T.A transversions. We find that the mutator phenotype of a mutY strain can be fully complemented by overexpressing MutM protein (Fpg protein) from a plasmid clone. The MutM protein removes 8-oxoG lesions from DNA. In addition, we have isolated a strain with a chromosomal mutation that suppresses the mutY phenotype and found that this suppressor also overexpresses MutM. Finally, a mutY mutM double mutant has a 25- to 75-fold higher mutation rate than either mutator alone. The data strongly suggest that MutY is part of an intricate repair system directed against 8-oxoG lesions in nucleic acids and that the primary function of MutY in vivo is the removal of adenines that are misincorporated opposite 8-oxoG lesions during DNA synthesis.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of California, Los Angeles 90024.
authors.forename: M L
authors.initials: ML
authors.lastname: Michaels
authors.forename: C
authors.initials: C
authors.lastname: Cruz
authors.forename: A P
authors.initials: AP
authors.lastname: Grollman
authors.forename: J H
authors.initials: JH
authors.lastname: Miller
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001482:Base Composition; D001483:Base Sequence; D004249:DNA Damage; D045647:DNA Glycosylases; D004260:DNA Repair; D004261:DNA Replication; D043382:DNA-Formamidopyrimidine Glycosylase; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D006147:Guanine / Q000031:analogs & derivatives*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000235:genetics / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis; D010957:Plasmids
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D009838:Oligodeoxyribonucleotides; C024829:8-hydroxyguanine; D006147:Guanine; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; C061738:mutY adenine glycosylase; D043382:DNA-Formamidopyrimidine Glycosylase; C468610:DNA-formamidopyrimidine glycosylase, E coli