title: Segment-specific mutagenesis: extensive mutagenesis of a lac promoter/operator element.
abstract: A method for highly efficient segment-specific mutagenesis is described. The method uses as target for sodium bisulfite mutagenesis the DNA single strands of a DNA restriction fragment that had been separated by cloning into base-complementary regions of a pair of phage fd vectors. After repair synthesis in vitro, the mutagenized DNA fragment is recovered by cloning into a nonmutated plasmid vector and analyzed for sequence and by functional tests. By using this method, the nucleotide sequence of a 109-base pair restriction fragment containing the lac promoter/operator from Escherichia coli was extensively modified. More than 90% of the 235 isolates obtained showed a change in phenotype; all of 22 analyzed for their nucleotide sequence were found to carry multiple C leads to T point mutations in up to 60% of the possible target positions. Nevertheless, few isolates showed major changes in promoter activity relative to the nonmutated promoter element, which indicates a high degree of flexibility in the promoter sequence.
mesh_terms: D001483:Base Sequence; D004274:DNA, Recombinant; D004926:Escherichia coli / Q000235:genetics; D007763:Lac Operon; D009154:Mutation; D009876:Operon; D010957:Plasmids; D013447:Sulfites
chemical_list: D004274:DNA, Recombinant; D013447:Sulfites; C009279:sodium bisulfite