DNA-strand Breaks in Two Strains of Escherichia Coli after Exposure to γ-rays

Summary

A progressive decrease in the sedimentation rate of the DNA from Escherichia coli, wild type (parent strain), and the radioresistant mutant 6γ, indicating single-strand breaks in double-stranded DNA, was obtained after exposure of the strains to an increasing dose of γ-rays. Sedimentation of the DNA from irradiated cells of E. coli 6γ was restored to the pre-irradiation rate after a period of post-irradiation growth. No such effect was obtained with irradiated cells of the parent strain. Amino-acid starvation or addition of chloramphenicol after irradiation inhibited the restoration of the sedimentation rate of DNA.