title: Spectra of spontaneous mutations in Escherichia coli strains defective in mismatch correction: the nature of in vivo DNA replication errors.
abstract: We have determined the DNA sequence changes in 487 spontaneous mutations in the N-terminal part of the lacI gene in mutH, mutL, and mutS strains of Escherichia coli. These strains display elevated spontaneous mutation rates because of a deficiency in the process of postreplicative mismatch correction. As a consequence the mutational spectra reveal the nature of spontaneous DNA replication errors. The spectra consist of base substitutions (75%) and single-base deletions (25%). Among the base substitutions, transitions (both A.T----G.C and G.C----A.T) are strongly favored over transversions (96% versus 4%). Large site-to-site differences are observed among identical base substitutions, presumably reflecting the modulating effects of neighboring bases. The single-base-deletion spectrum is dominated by a large hotspot at a run of adjacent identical base pairs, implying a Streisinger-slippage mechanism. The data, when compared to a previously determined wild-type spectrum, also provide information on the specificity of the mismatch repair system.
authors.forename: R M
authors.initials: RM
authors.lastname: Schaaper
authors.forename: R L
authors.initials: RL
authors.lastname: Dunn
mesh_terms: D001483:Base Sequence; D002872:Chromosome Deletion; D004260:DNA Repair; D004261:DNA Replication; D004269:DNA, Bacterial / Q000096:biosynthesis / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D009154:Mutation
chemical_list: D004269:DNA, Bacterial