OCCURRENCE OF SUPPRESSORS IN CAFFEINE-RESISTANT MUTANTS FROM E COLI K12

Mutants resistant to lethal concentrations of caffeine (CafR) were derived from Escherichia coli K12. Caffeine resistance conferred on the mutants enhanced by a factor of 1.1-2.2 the resistance spontaneously shown by the wild-type strain. Caffeine was not found to behave as a purine analogue in the biosynthetic pathway of purines. Neither cross-resistance to other purine analogues nor excretion or requirement in purine bases was observed. Caffeine-resistant bacteria derived from UV repair deficient strains appeared to acquire an increased resistance to UV irradiation. Some of these mutants could partially repair the UV damage produced in the bacterial DNA whereas for phage DNA they were either fully or not at all able to perform host-cell reactivation of UV-irradiated phage λ. In some CafR mutants there was a correlation between acquisition of caffeine resistance and suppression. About 80% of CafR mutants derived from E. coli K12 substrain 112-12 carried the amber suppressor su-II+. It is suggested that selection of CafR mutants might be a way of collecting bacteria with suppressors. © 1969.