title: Specific binding of human MSH2.MSH6 mismatch-repair protein heterodimers to DNA incorporating thymine- or uracil-containing UV light photoproducts opposite mismatched bases.
abstract: Previous studies have demonstrated recognition of DNA-containing UV light photoproducts by bacterial (Feng, W.-Y., Lee, E., and Hays, J. B. (1991) Genetics 129, 1007-1020) and human (Mu, D., Tursun, M., Duckett, D. R., Drummond, J. T., Modrich, P., and Sancar, A. (1997) Mol. Cell. Biol. 17, 760-769) long-patch mismatch-repair systems. Mismatch repair directed specifically against incorrect bases inserted during semi-conservative DNA replication might efficiently antagonize UV mutagenesis. To test this hypothesis, DNA 51-mers containing site-specific T-T cis-syn-cyclobutane pyrimidine-dimers or T-T pyrimidine-(6-4')pyrimidinone photoproducts, with all four possible bases opposite the respective 3'-thymines in the photoproducts, were analyzed for the ability to compete with radiolabeled (T/G)-mismatched DNA for binding by highly purified human MSH2.MSH6 heterodimer protein (hMutSalpha). Both (cyclobutane-dimer)/AG and ((6-4)photoproduct)/AG mismatches competed about as well as non-photoproduct T/T mismatches. The two respective pairs of photoproduct/(A(T or C)) mismatches also showed higher hMutSalpha affinity than photoproduct/AA "matches"; the apparent affinity of hMutSalpha for the ((6-4)photoproduct)/AA-"matched" substrate was actually less than that for TT/AA homoduplexes. Surprisingly, although hMutSalpha affinities for both non-photoproduct UU/GG double mismatches and for (uracil-cyclobutane-dimer)/AG single mismatches were high, affinity for the (uracil-cyclobutane-dimer)/GG mismatch was quite low. Equilibrium binding of hMutSalpha to DNA containing (photoproduct/base) mismatches and to (T/G)-mismatched DNA was reduced similarly by ATP (in the absence of magnesium).
authors.affiliation: Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon 97331-7301, USA. haysj@bcc.orst.edu
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.forename: C W
authors.initials: CW
authors.lastname: Lawrence
authors.forename: G M
authors.initials: GM
authors.lastname: Li
authors.forename: J B
authors.initials: JB
authors.lastname: Hays
mesh_terms: D020137:Base Pair Mismatch; D004247:DNA / Q000528:radiation effects*; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D006801:Humans; D008957:Models, Genetic; D051718:MutS Homolog 2 Protein; D016296:Mutagenesis; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D011740:Pyrimidine Dimers; D013941:Thymine; D014466:Ultraviolet Rays; D014498:Uracil
chemical_list: D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; D011518:Proto-Oncogene Proteins; D011740:Pyrimidine Dimers; D014498:Uracil; D004247:DNA; C497172:MSH2 protein, human; D051718:MutS Homolog 2 Protein; D013941:Thymine