Abstract | BACKGROUND: The current investigation was undertaken to determine key steps differentiating G:T and G:A repair at the H-ras oncogenic hot spot within the nuclear environment because of the large difference in repair efficiency of these two mismatches. RESULTS: Electrophoretic mobility shift (gel shift) experiments demonstrate that DNA containing mismatched bases are recognized and bound equally efficiently by hMutSalpha in both MMR proficient and MMR deficient (hMLH1-/-) nuclear extracts. Competition experiments demonstrate that while hMutSalpha predictably binds the G:T mismatch to a much greater extent than G:A, hMutSalpha demonstrates a surprisingly equal ratio of competitive inhibition for both G:T and G:A mismatch binding reactions at the H-ras hot spot of mutation. Further, mismatch repair assays reveal almost 2-fold higher efficiency of overall G:A repair (5'-nick directed correct MMR to G:C and incorrect repair to T:A), as compared to G:T overall repair. Conversely, correct MMR of G:T --> G:C is significantly higher (96%) than that of G:A --> G:C (60%). CONCLUSION: Combined, these results suggest that initiation of correct MMR requires the contribution of two separate steps; initial recognition by hMutSalpha followed by subsequent binding. The 'avidity' of the binding step determines the extent of MMR pathway activation, or the activation of a different cellular pathway. Thus, initial recognition by hMutSalpha in combination with subsequent decreased binding to the G:A mismatch (as compared to G:T) may contribute to the observed increased frequency of incorrect repair of G:A, resulting in the predominant GGC --> GTC ( Gly --> Val) ras-activating mutation found in a high percentage of human tumors.
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Authors | Michael Edelbrock, Huiling He, Allen Schroering, Martha Fernstrom, Sangeetha Bathala, Kandace J Williams |
Journal | BMC molecular biology
(BMC Mol Biol)
Vol. 6
Pg. 6
(Mar 14 2005)
ISSN: 1471-2199 [Electronic] England |
PMID | 15766387
(Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, P.H.S.)
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Chemical References |
- Codon
- DNA-Binding Proteins
- Proteins
- DNA
- ras Proteins
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Topics |
- Base Pair Mismatch
(genetics)
- Cell Line, Tumor
- Codon
(genetics)
- DNA
(metabolism)
- DNA Repair
- DNA-Binding Proteins
(genetics, metabolism)
- Electrophoretic Mobility Shift Assay
(methods)
- HCT116 Cells
- Humans
- Models, Biological
- Plasmids
(genetics)
- Point Mutation
(genetics)
- Proteins
(genetics)
- Proto-Oncogenes
(genetics)
- ras Proteins
(genetics)
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