Ultraviolet irradiation and cyclic AMP treatment produce a synergistic effect on the induction of the cle1 gene (coding for bacteriocin ColE1) in wild-type strains of Escherichia coli. On the other hand, cyclic AMP does not affect the uv-mediated induction of the recA, sfiA, and umuDC genes. Growth in the presence of glucose or glycerol does not affect the factor of amplification of the expression of the cle1 gene in uv-irradiated cells of the wild-type strain. Although, in cultures not treated with uv, the basal level of cle1 induction is about twice as high in cell grown grown with glycerol as in those using glucose as carbon source. In recA mutants neither simultaneous nor separate treatments with either cyclic AMP or uv irradiation induced transcription of the cle1 gene. Moreover, cyclic AMP induced a slight increase in cle1 gene expression in uv-irradiated cya strains, but not in the crp mutants. Nevertheless, the pattern of the uv-mediated induction of other SOS genes, such as umuDC, was the same in the cya and crp mutants, as in their parental wild-type strains. Furthermore, the uv-mediated induction of lambda prophage was decreased after either addition of cyclic AMP or growth in cultural conditions where the level of this nucleotide was low.