SUMMARY: A radiosensitive mutant of strain K12, W3747 was found to be similar to strains b and s with respect to survival following ultraviolet irradiation, plating-medium recovery, ability to ‘reactivate’ irradiated T1 phage, and in its cross-resistance pattern with radiomimetic chemicals. In all these respects the radiosensitive strain K12, AB1186, isolated by Howard-Flanders, was found to resemble the Hill radiation hypersensitive strain B, and, except in the ability to reactivate irradiated T1 phage, strain B. Strains W3747 and AB1886 acquired sensitivity to radiomimetic chemicals concomitantly with radiation sensitivity. Strains B and B on becoming hypersensitive to radiation did not become correspondingly hypersensitive to radiomimetic chemicals. In fact, they acquired a small degree of resistance to these chemicals, relative to strain B, and a substantial increase in resistance to 1-methyl-3-nitro-1-nitrosoguanidine and proflavine. These results are discussed in terms of known genetic loci implicated in radiation sensitivity and resistance.


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