Schizosaccharomyces pombeMutSα and MutLα Maintain Stability of Tetra-Nucleotide Repeats and Msh3 of Hepta-Nucleotide Repeats.
Defective mismatch repair (MMR) in humans is associated with colon cancer and instability of microsatellites, that is, DNA sequences with one or several nucleotides repeated. Key factors of eukaryotic MMR are the heterodimers MutSα (Msh2-Msh6), which recognizes base-base mismatches and unpaired nucleotides in DNA, and MutLα (Mlh1-Pms1), which facilitates downstream steps. In addition, MutSβ (Msh2-Msh3) recognizes DNA loops of various sizes, although our previous data and the data presented here suggest that Msh3 ofSchizosaccharomyces pombedoes not play a role in MMR. To test microsatellite stability inS. pombeand hence DNA loop repair, we have inserted tetra-, penta-, and hepta-nucleotide repeats in theade6gene and determined their Ade+reversion rates and spectra in wild type and various mutants. Our data indicate that loops with four unpaired nucleotides in the nascent and the template strand are the upper limit of MutSα- and MutLα-mediated MMR inS. pombeStability of hepta-nucleotide repeats requires Msh3 and Exo1 in MMR-independent processes as well as the DNA repair proteins Rad50, Rad51, and Rad2FEN1Most strikingly, mutation rates in the double mutantsmsh3 exo1andmsh3 rad51were decreased when compared to respective single mutants, indicating that Msh3 prevents error prone processes carried out by Exo1 and Rad51. We conclude that Msh3 has no obvious function in MMR inS. pombe, but contributes to DNA repeat stability in MMR-independent processes.
North West Cancer Research Institute, School of Medical Sciences, Bangor University, LL57 2UW, UK.
Desirée
0000-0003-4072-6159
D
Villahermosa
Strain Development LBPE38, Lonza, CH-3930 Visp, Switzerland.
Olaf
O
Christensen
North West Cancer Research Institute, School of Medical Sciences, Bangor University, LL57 2UW, UK.
Karen
K
Knapp
North West Cancer Research Institute, School of Medical Sciences, Bangor University, LL57 2UW, UK o.fleck@bangor.ac.uk.
Oliver
0000-0003-0550-6513
O
Fleck
D053843:DNA Mismatch Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D042822:Genomic Instability; D018895:Microsatellite Repeats; D000070956:MutL Proteins / Q000235:genetics / Q000378:metabolism*; D000074081:MutS Homolog 3 Protein / Q000235:genetics / Q000378:metabolism*; D059645:Mutation Rate; D051135:Rad51 Recombinase / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism
D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; D000074081:MutS Homolog 3 Protein; C084232:RHP51 protein, S pombe; C480032:Rad50 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D051135:Rad51 Recombinase; D004706:Endodeoxyribonucleases; C445562:Rad2 protein, S pombe; D000070956:MutL Proteins
FEN1; homologous recombination repair; microsatellite instability; mismatch repair; repetitive DNA