Deletion of genes for adenylate cyclase (delta cya) or cAMP receptor protein (delta crp) in E. coli K-12 confers a phenotype that includes resistance to UV radiation (254 nm). Such mutations lead to UV resistance of uvr+, uvrA, lexA and recA strains which could partly be abolished by the addition of cAMP to delta cya but not to delta crp strain culture medium. This effect was not related to either inducibility of major DNA repair genes or growth rate of the bacteria. Enhanced survival was also observed for UV-irradiated lambda bacteriophage indicating that a repair mechanism of UV lesions was involved in this phenomenon.