Analysis of photoenzymatic repair of UV lesions in DNA by single light flashes IX. Excess production of photoreactivating enzyme in E. Coli B s-1-160 under different growth conditions, and its suppression by adenine

Abstract

Summary The extent of photoenzymatic repair resulting from a single light flash is determined by the number of photoreactivating enzyme (PRE) molecules present within cells. This permitted us to study the dependence of PRE production on growth conditions in E. coli B s-1 -160 (an adenine-requiring mutant of strain B s-1 with about a 6-fold increased PRE content), and to compare it with that of the parental strain B s-1 . The excess PRE production was observed only in B s-1 -160 cells entering the stationary phase; their PRE content during exponential growth differed little from that in B s-1 . Supplementation of broth with adenine at concentrations from 40 to 200 μg/ml progressively decreases the amount of PRE present in stationary phase B s-1 -160 cells, but does not affect the PRE content of B s-1 cells. The same effect was observed with several adenine analogues and related substances, some of them unable to support growth of B s-1 -160 in minimal media. The results indicate that excess PRE production occurs only under conditions of severe adenine shortage, i.e. when growth of adenine-requiring cells comes to a halt due to exhaustion of the adenine supply. This suggests that adenine or some related compound is involved in a regulatory mechanism responsible for the low level of PRE production that is characteristic of E. coli .