Gap formation is associated with methyl-directed mismatch correction under conditions of restricted DNA synthesis.
A covalently closed, circular heteroduplex containing a G-T mismatch and a single hemimethylated d(GATC) site is subject to efficient methyl-directed mismatch correction in Escherichia coli extracts when repair DNA synthesis is severely restricted by limiting the concentration of exogenously supplied deoxyribonucleoside-5'-triphosphates or by supplementing reactions with chain-terminating 2',3'-dideoxynucleoside triphosphates. However, repair under these conditions results in formation of a single-strand gap in the region of the molecule containing the mismatch and the d(GATC) site. These findings indicate that repair DNA synthesis required for methyl-directed correction can initiate in the vicinity of the mispair, and they are most consistent with a repair reaction involving 3'----5' excision (or strand displacement) from the d(GATC) site followed by 5'----3' repair DNA synthesis initiating in the vicinity of the mismatch.
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Department of Biochemistry, Duke University Medical Center, Durham, NC 27710.
Grilley
M
M
Thresher
R
R
Griffith
J
J
Modrich
P
P
D004260:DNA Repair / Q000235:genetics / Q000502:physiology*; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000648:ultrastructure; D003854:Deoxyribonucleotides / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics; D008745:Methylation; D008854:Microscopy, Electron; D009154:Mutation; D015183:Restriction Mapping
D004277:DNA, Single-Stranded; D003854:Deoxyribonucleotides