Repression of UV induction of lambda prophage by caffeine.

Caffeine was found to function as a repressor of UV-induced lambda prophage when added to the post-irradiation culture medium with both uvrB+ and uvrB- strains of E. coli K12. Caffeine functioned as a repressor of lambda induction at high but not low inducing doses of UV. Caffeine alone at concentrations above 10 mg/plate functioned as an inducer of lambda prophage.