Thymineless Radiosensitization in Escherichia coli

Abstract

In a previous communication (1), it was reported that, when purine-requiring strains of Escherichia coli are starved for natural purines, they develop a threefold increase in sensitivity to the lethal effects of X-rays, without a concomitant change in UV sensitivity. The transition from the normal to the sensitized state was found to be an all-or-none phenomenon which followed exponential kinetics, with a halftime of about 16 minutes. The sensitized state was completely reversible by purine supplementation, and reversal appeared to antedate cell replication. It was thought of interest to investigate the influence of simultaneous thymine or thymidine starvation on the development of purineless radiosensitization. During the course of these studies, it was discovered that similar radiosensitization could be induced by cultivation in the absence of thymine or thymidine. Moreover, since the multiple auxotroph used for these studies also required exogenous tryptophan, it was possible to examine the influence of tryptophan starvation on the survival and radiosensitivity of purineand thymidine-starved cells.