title: Apn1 and Apn2 endonucleases prevent accumulation of repair-associated DNA breaks in budding yeast as revealed by direct chromosomal analysis.
abstract: Base excision repair (BER) provides relief from many DNA lesions. While BER enzymes have been characterized biochemically, BER functions within cells are much less understood, in part because replication bypass and double-strand break (DSB) repair can also impact resistance to base damage. To investigate BER in vivo, we examined the repair of methyl methanesulfonate (MMS) induced DNA damage in haploid G1 yeast cells, so that replication bypass and recombinational DSB repair cannot occur. Based on the heat-lability of MMS-induced base damage, an assay was developed that monitors secondary breaks in full-length yeast chromosomes where closely spaced breaks yield DSBs that are observed by pulsed-field gel electrophoresis. The assay detects damaged bases and abasic (AP) sites as heat-dependent breaks as well as intermediate heat-independent breaks that arise during BER. Using a circular chromosome, lesion frequency and repair kinetics could be easily determined. Monitoring BER in single and multiple glycosylase and AP-endonuclease mutants confirmed that Mag1 is the major enzyme that removes MMS-damaged bases. This approach provided direct physical evidence that Apn1 and Apn2 not only repair cellular base damage but also prevent break accumulation that can result from AP sites being channeled into other BER pathway(s).
authors.affiliation: Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences (NIH, DHHS), Research Triangle Park, NC 27709, USA.
authors.forename: Wenjian
authors.initials: W
authors.lastname: Ma
authors.forename: Michael A
authors.initials: MA
authors.lastname: Resnick
authors.forename: Dmitry A
authors.initials: DA
authors.lastname: Gordenin
mesh_terms: D015825:Chromosomes, Fungal; D053903:DNA Breaks, Double-Stranded; D045647:DNA Glycosylases / Q000502:physiology; D004260:DNA Repair; D045643:DNA Repair Enzymes; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics / Q000502:physiology*; D016521:Electrophoresis, Gel, Pulsed-Field; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000502:physiology*; D016193:G1 Phase / Q000235:genetics; D017353:Gene Deletion; D006358:Hot Temperature; D008741:Methyl Methanesulfonate / Q000633:toxicity; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D008741:Methyl Methanesulfonate; D004706:Endodeoxyribonucleases; C083274:Apn1 protein, S cerevisiae; D045647:DNA Glycosylases; C445668:MAG1 protein, S cerevisiae; C468953:APN2 protein, S cerevisiae; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D045643:DNA Repair Enzymes