Breakage of DNA in Rec+ and Rec- Bacteria by Disintegration of Radiophosphorous Atoms in DNA and Possible Cause of Pleiotropic Effects of RecA Mutation

Bacteriophages lose their infectivity upon disintegration of 32P atoms incorporated in their DNA (Hershey et al., 1951). The kinetics of inactivation of a population of radioactive phage particles, each containing N atoms of phosphorus initially labeled with 32P at a specific activity A0 mc/mg P can be expressed by the relation log10S = −1.48 × 10−6 A0αN(1 − e−λt) in which S is the surviving fraction and λ the fractional disintegration of 32P per day. A plot of log10S vs. (1 − e−λt), the fraction of the initial 32P atoms disintegrated by the tth day, is therefore a straight line with slope proportional to A0αN. From the slope can be calculated the value of α, the fraction of 32P disintegrations which are lethal or the efficiency of killing of 32P disintegration. The value of α for phages with double-stranded DNA is much less than 1, showing that only a certain...