DNA-substrate sequence specificity of human G:T mismatch repair activity.
G:T mispairs in DNA originate spontaneously via deamination of 5-methylcytosine. Such mispairs are restored to normal G:C pairs by both E. coli K strains and human cells. In this study we have analyzed the repair by human cell extracts of G:T mismatches in various DNA contexts. We performed two sets of experiments. In the first, repair was sequence specific in that G:T mispairs at CpG sites at four different CpG sites were repaired, but a G:T mismatch at a GpG site was not. Cytosine hemimethylation did not block repair of a substrate containing a CpG/GpT mismatch. In the second set of experiments, substrates with a G:T mismatch at a fixed position were constructed with an A, T, G, or C 5' to the mismatched G, and alterations in the complementary strand to allow otherwise perfect Watson-Crick pairing. All were incised just 5' to the mismatched T and competed for repair incision with a G:T substrate in which a C was 5' to the mismatched G. Thus human G:T mismatch activity shows sequence specificity, incising G:T mismatched pairs at some DNA sites, but not at others. At an incisable site, however, incision is little influenced by the base 5' to the mismatched G.
Sibghat-Ullah
Department of Medicine, Cross Cancer Institute, Edmonton, Alberta, Canada.
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D001482:Base Composition; D001483:Base Sequence; D001667:Binding, Competitive; D002460:Cell Line; D002474:Cell-Free System; D004247:DNA / Q000378:metabolism*; D004260:DNA Repair; D006151:Guanosine; D006801:Humans; D008969:Molecular Sequence Data; D009692:Nucleic Acid Heteroduplexes; D013941:Thymine
D009692:Nucleic Acid Heteroduplexes; D006151:Guanosine; D004247:DNA; D013941:Thymine