The genetic constitution of the radiation-sensitive mutant Escherichia coli Bs-1.

Abstract

Abstract The radiation-sensitive strains Escherichia coli B s−1 and B s−1 are both unable to repair UV and X-ray damage in their DNA; in addition the B s−1 strain is also unable to repair certain UV-irradiated bacteriophages. In this respect the latter strain resembles Hcr − mutants of E. coli K12 strains, which are also UV sensitive, but, in contrast to E. coli B s−1 , X-ray resistant. By means of transduction analysis with phage P1kc it is shown that strain B s−1 is in fact a double mutant, carrying an Hcr − -like mutation, located on the chromosome near the gal locus, and a second mutation near met 3 , denoted exr − , which is responsible for the X-ray sensitivity. Both mutations influence the UV sensitivity of the B s−1 strain. The B s−2 mutant contains the exr − mutation only, which also accounts for the UV sensitivity of this strain.