Contribution of Various Types of Damage to Inactivation of Bacteriophage PM2 DNA in Frozen Solution by Gamma-radiation

Summary

When biologically-active double-stranded circular DNA of the bacteriophage PM2 in a solution of nutrient broth is irradiated at −196°C by ⁶⁰Co gamma-rays, about 85 per cent of the inactivation is due to nucleotide damage, i.e. damage in the nucleotides not associated with a chain break. Double-strand breaks contribute some 10 per cent to lethality and single-strand breaks only a minor fraction, if at all. About 10 per cent of the nucleotide damage that is lethal if present in single-stranded DNA is lethal in the double-stranded PM2 DNA. These results do not show large differences from those obtained previously for irradiation of PM2 DNA under conditions of indirect effect.