Methyl-directed repair of frameshift heteroduplexes in cell extracts from Escherichia coli.
The methyl-directed DNA repair efficiency of a series of M13mp9 frameshift heteroduplexes 1, 2, or 3 unpaired bases was determined by using an in vitro DNA mismatch repair assay. Repair of hemimethylated frameshift heteroduplexes in vitro was directed to the unmethylated strand; was dependent on MutH, MutL, and MutS; and was equally efficient on base insertions and deletions. However, fully methylated frameshift heteroduplexes were resistant to repair, while totally unmethylated substrates were repaired with no strand bias. Hemimethylated 1-, 2-, or 3-base insertion and deletion heteroduplexes were repaired by the methyl-directed mismatch repair pathway as efficiently as the G.T mismatch. These results are consistent with earlier in vivo studies and demonstrate the involvement of methyl-directed DNA repair in the efficient prevention of frameshift mutations.
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Department of Microbiology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Grafstrom
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D001482:Base Composition; D001483:Base Sequence; D002872:Chromosome Deletion; D003001:Cloning, Molecular; D003090:Coliphages / Q000235:genetics*; D004260:DNA Repair; D004269:DNA, Bacterial / Q000235:genetics*; D004279:DNA, Viral / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D005798:Genes, Bacterial; D008745:Methylation; D008969:Molecular Sequence Data; D009154:Mutation; D009692:Nucleic Acid Heteroduplexes / Q000235:genetics*
D004269:DNA, Bacterial; D004279:DNA, Viral; D009692:Nucleic Acid Heteroduplexes