title: Ntg1p, the base excision repair protein, generates mutagenic intermediates in yeast mitochondrial DNA.
abstract: Mitochondrial DNA is predicted to be highly prone to oxidative damage due to its proximity to free radicals generated by oxidative phosphorylation. Base excision repair (BER) is the primary repair pathway responsible for repairing oxidative damage in nuclear and mitochondrial genomes. In yeast mitochondria, three N-glycosylases have been identified so far, Ntg1p, Ogg1p and Ung1p. Ntg1p, a broad specificity N-glycosylase, takes part in catalyzing the first step of BER that involves the removal of the damaged base. In this study, we examined the role of Ntg1p in maintaining yeast mitochondrial genome integrity. Using genetic reporters and assays to assess mitochondrial mutations, we found that loss of Ntg1p suppresses mitochondrial point mutation rates, frameshifts and recombination rates. We also observed a suppression of respiration loss in the ntg1-Delta cells in response to ultraviolet light exposure implying an overlap between BER and UV-induced damage in the yeast mitochondrial compartment. Over-expression of the BER AP endonuclease, Apn1p, did not significantly affect the mitochondrial mutation rate in the presence of Ntg1p, whereas Apn1p over-expression in an ntg1-Delta background increased the frequency of mitochondrial mutations. In addition, loss of Apn1p also suppressed mitochondrial point mutations. Our work suggests that both Ntg1p and Apn1p generate mutagenic intermediates in the yeast mitochondrial genome.
authors.affiliation: Department of Biology, University of Rochester, NY 14627-0211, USA.
authors.forename: Naina
authors.initials: N
authors.lastname: Phadnis
authors.forename: Reema
authors.initials: R
authors.lastname: Mehta
authors.forename: Nida
authors.initials: N
authors.lastname: Meednu
authors.forename: Elaine A
authors.initials: EA
authors.lastname: Sia
mesh_terms: D001483:Base Sequence; D045647:DNA Glycosylases / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004271:DNA, Fungal / Q000235:genetics* / Q000378:metabolism*; D004272:DNA, Mitochondrial / Q000235:genetics* / Q000378:metabolism*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D016368:Frameshift Mutation; D015870:Gene Expression; D016681:Genome, Fungal; D008954:Models, Biological; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D017354:Point Mutation; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism* / Q000528:radiation effects; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D004271:DNA, Fungal; D004272:DNA, Mitochondrial; D029701:Saccharomyces cerevisiae Proteins; D004706:Endodeoxyribonucleases; C083274:Apn1 protein, S cerevisiae; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; C505160:Ogg1 protein, S cerevisiae; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; C101825:NTG1 protein, S cerevisiae; D045643:DNA Repair Enzymes; D010100:Oxygen