The expression of the gene encoding colicin E1, cea, was studied in Escherichia coli by using cea-lacZ gene fusions. Expression of the fusions showed the same characteristics as those of the wild-type cea gene: induction by treatments that damage DNA and regulation by the SOS response, sensitivity to catabolite repression, and a low basal level of expression, despite the presence of the fusion in a multicopy plasmid. Induction of expression by DNA-damaging treatments was found to differ from other genes involved in the SOS response (exemplified by recA), in that higher levels of DNA damage were required and expression occurred only after a pronounced delay. The delay in expression following an inducing treatment was more pronounced under conditions of catabolite repression, indicating that the cyclic AMP-cyclic AMP receptor protein complex may play a role in induction. These observations also suggest a biological rationale for the control of cea expression by the SOS response and the cyclic AMP-cyclic AMP receptor protein catabolite repression system
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