Mapping and disruption of the chpB locus in Escherichia coli.

The chpB locus is a chromosomal homolog of the pem locus, which is responsible for stable maintenance of plasmid R100 within the host cells. Like pem, chpB codes for two genes, chpBK and chpBI, encoding a growth inhibitor and a suppressor for the killing action of the ChpBK protein, respectively. Here, we determined the precise location of the chpB locus, which is linked to ileR and ppa in the order ileR-chpB-ppa, at 95.7 min on the map of Escherichia coli. We then constructed mutants with an insertion of a (cat) fragment within chpBK or chpBI on the E. coli chromosome. These mutants grew normally, indicating that chpB is dispensable for cell growth.