THIOLS, RECA INDUCTION AND RADIOSENSITIVITY IN ESCHERICHIA-COLI

Induction by gamma-radiation, UV radiation or hydroxyurea of RecA gene product synthesis in Escherichia coli, monitored as beta-D-galactosid ase in recA-lacZ fusion strains, was shown to be inhibited if 2-mercap toethylamine (MEA) was added before treatment with the inducing agents . If cysteine (Cys) at low concentrations was added at the same time a s MEA it counteracted the action of MEA. The effect of MEA may be desc ribed as a competitive inhibition of an inducing or conducting effect of Cys. In E. coli GE499 (uvrA(+)), complete inhibition by 30-mmol dm( -3) MEA of recA induction was associated with about five times higher radio-resistence. Both of these effects of MEA were completely reverse d by 0.3-mmol dm(-3) Cys. As shown in parallel experiments with E. col i GE500 (uvrA(-)), these effects of MEA and Cys were shown to be indep endent of excision-repair proficiency. Treatment of bacteria with MEA and/or Cys was shown not to lead to increased intracellular concentrat ions of these thiols. Instead, treatment with them appeared to provoke conspicuous increases in glutathione levels, which are, however, prob ably not directly involved in the studied action of MEA and Cys.