"Mutational synergism" of ultraviolet light and caffeine in Escherichia coli.

Shankel, Delbert M. (University of Kansas, Lawrence). "Mutational synergism" of ultraviolet light and caffeine in Escherichia coli. J. Bacteriol. 84:410-415. 1962.-When ultraviolet-induced mutations of Escherichia coli B/r develop in the presence of caffeine, there is a large increase in mutant numbers. The development of these "extra" mutants is not affected by the presence of normally occurring purines and pyrimidines, azauracil, azathymine, or 5-methyltryptophan, but many of the mutants can be photoreversed. They are "stabilized" or "lost" during the first hour of postirradiation growth. Enzymatically active materials extracted from E. coli cells do not interfere with the caffeine effect, and variation of the growth temperature during the development of the mutations fails to alter the effect. "Prefeeding" the cells with caffeine prior to irradiation does not produce the response. The effect is observable with both stationary-phase and log-phase populations, but is not observable when a relatively high dosage of ultraviolet light is employed.