Identification and genetic analysis of sbcC mutations in commonly used recBC sbcB strains of Escherichia coli K-12

Evidence is presented to show that Escherichia coli JC7618, JC7621, and JC7623, previously regarded as having a recB recC sbcB genotype, carry an additional mutation in a new gene designated sbcC at minute 9 on the standard genetic map. In the absence of the sbcC mutation these strains are sensitive to mitomycin C and have a reduced efficiency of recombination. Cultures of recBC sbcB (sbcC+) strains grow slowly, contain many inviable cells, and rapidly accumulate fast-growing variants due to mutation of sbcC. sbcC has been identified on recombinant plasmids and tentatively located by Tn1000 mutagenesis to a 0.9-kilobase DNA section between proC and phoR.