title: Schizosaccharomyces pombe encodes a mutated AP endonuclease 1.
abstract: Mutagenic and cytotoxic apurinic/apyrimidinic (AP) sites are among the most frequent lesions in DNA. Repair of AP sites is initiated by AP endonucleases and most organisms possess two or more of these enzymes. Saccharomyces cerevisiae has AP endonuclease 1 (Apn1) as the major enzymatic activity with AP endonuclease 2 (Apn2) being an important backup. Schizosaccharomyces pombe also encodes two potential AP endonucleases, and Apn2 has been found to be the main repair activity, while Apn1 has no, or only a limited role in AP site repair. Here we have identified a new 5' exon (exon 1) in the apn1 gene and show that the inactivity of S. pombe Apn1 is due to a nonsense mutation in the fifth codon of this new exon. Reversion of this mutation restored the AP endonuclease activity of S. pombe Apn1. Interestingly, the apn1 nonsense mutation was only found in laboratory strains derived from L972 h(-) and not in unrelated isolates of S. pombe. Since all S. pombe laboratory strains originate from L972 h(-), it appears that all experiments involving S. pombe have been conducted in an apn1(-) mutant strain with a corresponding DNA repair deficiency. These observations have implications both for future research in S. pombe and for the interpretation of previously conducted epistatis analysis.
authors.affiliation: Department of Microbiology, Oslo University Hospital HF Rikshospitalet, PO Box 4950 Nydalen, NO-0424 Oslo, Norway.
authors.forename: Jon K
authors.initials: JK
authors.lastname: Laerdahl
authors.forename: Hanne
authors.initials: H
authors.lastname: Korvald
authors.forename: Line
authors.initials: L
authors.lastname: Nilsen
authors.forename: Kristin
authors.initials: K
authors.lastname: Dahl-Michelsen
authors.forename: Torbjørn
authors.initials: T
authors.lastname: Rognes
authors.forename: Magnar
authors.initials: M
authors.lastname: Bjørås
authors.forename: Ingrun
authors.initials: I
authors.lastname: Alseth
mesh_terms: D000478:Alkylation; D000595:Amino Acid Sequence; D001483:Base Sequence; D003062:Codon / Q000235:genetics; D018389:Codon, Nonsense; D019295:Computational Biology; D017124:Conserved Sequence / Q000235:genetics; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000737:chemistry / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D043223:Deoxyribonuclease IV (Phage T4-Induced) / Q000378:metabolism; D004789:Enzyme Activation / Q000235:genetics; D004926:Escherichia coli / Q000166:cytology / Q000201:enzymology / Q000235:genetics; D005090:Exodeoxyribonucleases / Q000378:metabolism; D005091:Exons / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010641:Phenotype; D017433:Protein Structure, Secondary; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D003062:Codon; D018389:Codon, Nonsense; D050505:Mutant Proteins; D029702:Schizosaccharomyces pombe Proteins; D005090:Exodeoxyribonucleases; C020133:exodeoxyribonuclease III; D043223:Deoxyribonuclease IV (Phage T4-Induced); C480730:Apn1 protein, S pombe; C480729:Apn2 protein, S pombe; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase