Induction of phr gene expression by irradiation of ultraviolet light in Escherichia coli.

To measure the degree of phr gene induction by DNA-damaging agents, the promoter region was fused to the coding region of the lacZ gene in plasmid pMC1403. The new plasmids were introduced into Escherichia coli cells having different repair capabilities. More efficient induction of phr gene expression was detected in a uvrA- strain as compared with the wild-type strain. In addition, obvious induction was detected in uvrA- cells treated by 4-nitroquinoline 1-oxide and mitomycin C. Nalidixic acid, an inhibitor of DNA gyrase, also induced phr gene expression. In contrast, little induced gene expression was noted in UV-irradiated lexA- and recA- strains. It is suggested from these results that induction of the phr gene is one of the SOS responses. Possible nucleotide sequences which could be considered to constitute an SOS box were found at the regulator region of the phr gene.