Competence mutants. 3. Responses to radiations.

Class 3 com(-) mutants [normal in deoxyribonucleic acid (DNA) uptake but poor in ability to transform] were investigated with regard to ultraviolet (UV) and X-ray sensitivity of colony-forming ability and with regard to their ability to be transformed by UV- and X-ray-irradiated DNA. Three mutants, com(-)40, 60, and 78, were highly UV-sensitive in colony-forming ability. None of the mutants was more sensitive than wild type to UV-irradiated transforming DNA; in fact, six of the mutants showed considerably greater resistance. Two of the mutants (com(-)40 and 60) were slightly more sensitive to X ray in colony formation, whereas most of the mutants showed some degree of sensitivity to X-ray-irradiated transforming DNA. In addition, the physical fate of X-ray-irradiated transforming DNA has been examined, and in one case (com(-)48) there was a significant drop in sedimentation value of X-ray-irradiated donor DNA after uptake by recipient cells. The com(-) mutants analyzed have been classified on the basis of their UV and X-ray sensitivities, and, where appropriate, possible biochemical lesions have been implicated.