Role of the colicin A lysis protein in the expression of the colicin A operon

The involvement of the cal gene, which encodes the colicin A lysis protein, in the expression of the colicin A operon is demonstrated. Colicin A synthesis by Escherichia coli was studied at various temperatures in cells containing either the wild-type colicin A operon or the colicin A operon with the cal gene deleted. The amount of colicin A produced was lower in cells containing the colicin A operon devoid of the cal gene than in wild-type cells, In cells treated with the antibiotic globomycin, the synthesis of colicin A was blocked in null cal mutants at all temperatures. It was blocked only at low temperature in cells containing the wild-type colicin A operon, but not in cells subjected to heat shock or azide treatment. The cal gene product may be an activator of colicin A expression and of its own expression. An unidentified product, possibly a heat-shock protein, may also be involved and could complement the cal gene product in some situations.