title: Elevated mutant frequencies and predominance of G:C to A:T transition mutations in Msh6(-/-) small intestinal epithelium.
abstract: The DNA mismatch repair (MMR) system is primarily responsible for purging newly synthesized DNA of errors incurred during semi-conservative replication. Lesion recognition is initially carried out by one of two heterodimeric protein complexes, MutS(alpha) or MutS(beta). While the former, comprised of MSH2 and MSH6, recognizes mispairs as well as short (1-2 nucleotide) insertions/deletions (IDLs), the latter, made up of MSH2 and MSH3, is primarily responsible for recognizing 2-6 nucleotide IDLs. As most of the functional information on these heterodimers is derived from in vitro studies, it was of interest to study the in vivo consequences of a lack of MutS(alpha). To this end, Big Blue( trade mark ) mice, that carry a lacI(+) transgenic lambda shuttle-phage mutational reporter, were crossed with Msh6(-/-) mice to evaluate the specific contribution of MutS(alpha) to genome integrity. Consistent with the importance of MutS(alpha) in lesion surveillance, small intestine epithelial cell DNA derived from lacI(+) Msh6(-/-) mice exhibited striking increases (average of 41-fold) in spontaneous mutant frequencies. Furthermore, the lacI gene mutation spectrum was dominated by G:C to A:T transitions, highlighting the critical importance of the MutS(alpha) complex in suppressing this frequently observed type of spontaneous mutation.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta, Canada T2N 4N1.
authors.forename: Sean C
authors.initials: SC
authors.lastname: Mark
authors.forename: Linda E
authors.initials: LE
authors.lastname: Sandercock
authors.forename: H Artee
authors.initials: HA
authors.lastname: Luchman
authors.forename: Agnes
authors.initials: A
authors.lastname: Baross
authors.forename: Winfried
authors.initials: W
authors.lastname: Edelmann
authors.forename: Frank R
authors.initials: FR
authors.lastname: Jirik
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D020137:Base Pair Mismatch; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000502:physiology*; D029968:Escherichia coli Proteins; D005656:Fungal Proteins; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism*; D056968:Lac Repressors; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D005656:Fungal Proteins; C094443:G-T mismatch-binding protein; D056968:Lac Repressors; C098790:MSH6 protein, S cerevisiae; C102997:Msh6 protein, mouse; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins