Radiation Response of Thymine-Starved Bacteria

Abstract

Different repair deficient thymine auxotrophs of Escherichia coli, collected at various periods of thymine starvation, have been studied for their sensitivity to X rays and ultraviolet light (uv). It has been found that depending on the strains selected, starvation could increase as well as decrease the subsequent radiation sensitivity. The cells which became resistant to X rays were also resistant to uv. The cells which became sensitive to uv were also sensitive to X rays. The cells which were prototrophic for their repair ability had their sensitivity increased due to thymine starvation; the cells which had defect in any steps of excision ability became resistant subsequent to thymine starvation. This increase in radiation resistance could be prevented by the presence of chloramphenicol during starvation and did not take place in cells which were rec A-. These results indicate the existence of an inducible repair system dependent upon the rec A gene.