title: Mismatch repair during pneumococcal transformation of small deletions produced by site-directed mutagenesis.
abstract: The genetic behaviour of short non-homologous regions has been studied during transformation of Streptococcus pneumoniae. Amethopterin-resistant mutants belonging to the amiA locus were used for these investigations. Five mutants deleted for 1-5 bp were obtained by oligonucleotide-directed mutagenesis. Their efficiency of transformation was measured using recipient strains either able to excise and repair mismatched bases (Hex+) or Hex- derivatives. Deletions or insertions of 1 and 2 bp are fully recognized by the Hex system, and are efficiently repaired whereas 3-bp deletions or insertions are only partially excised and repaired. The efficiency of repair is inversely related to the size of the non-homology. Markers with 5-bp deletions or insertions are poorly repaired and thus transform at very high frequency: similar results are obtained in reciprocal crosses. It is proposed that 1- or 2-bp deletions or insertions are included in the heteroduplex structure as transition mutations. The Hex system would detect only small deviations from the normal DNA structure.
mesh_terms: D002872:Chromosome Deletion; D002874:Chromosome Mapping; D004260:DNA Repair; D004269:DNA, Bacterial / Q000235:genetics; D004352:Drug Resistance, Microbial; D005798:Genes, Bacterial; D009154:Mutation; D009692:Nucleic Acid Heteroduplexes / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid; D013296:Streptococcus pneumoniae / Q000235:genetics*; D014170:Transformation, Genetic
chemical_list: D004269:DNA, Bacterial; D009692:Nucleic Acid Heteroduplexes