The Vsr endonuclease of Escherichia coli: an efficient DNA repair enzyme and a potent mutagen.
The Vsr endonuclease of Escherichia coli initiates the repair of T/G mismatches caused by deamination of 5-methylcytosine to thymine. In this paper, we examine the capacity of Vsr to prevent CG-to-TA mutations in cells with increased transcription of the cytosine methylase gene (dcm). We find that sufficient Vsr is produced by a single chromosomal copy of vsr to prevent mutagenesis. We also investigate the cause of the transition and frameshift mutations in cells overproducing Vsr. Neither the absence of the dcm methylase nor its overproduction affects Vsr-stimulated mutagenesis. However, addition of mutS, mutL, or mutH on multicopy plasmids has a significant effect: mutL or mutH decreases the number of mutations, while mutS stimulates mutagenesis. The mut-containing plasmids have the same effect in cells treated with 2-aminopurine and in cells made defective in DNA proofreading, two experimental situations known to cause transition and frameshift mutations by saturating mismatch repair.
Macintyre
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Biology Department, Concordia University, Montréal, Québec, Canada.
Doiron
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KM
Cupples
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CG
D000251:Adenosine Triphosphatases; D001426:Bacterial Proteins / Q000235:genetics; D002876:Chromosomes, Bacterial / Q000235:genetics; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000235:genetics; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics*; D029968:Escherichia coli Proteins; D005144:F Factor / Q000235:genetics; D016368:Frameshift Mutation; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; D009154:Mutation; D009876:Operon; D014169:Transformation, Bacterial
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C074770:MutL protein, E coli; D004248:DNA (Cytosine-5-)-Methyltransferases; D004706:Endodeoxyribonucleases; C059682:methyl-directed mismatch repair protein, E coli; C071421:vsr endonuclease; D000251:Adenosine Triphosphatases; D000070956:MutL Proteins; D051719:MutS DNA Mismatch-Binding Protein; C497175:MutS protein, E coli; D045643:DNA Repair Enzymes