SOME EFFECTS OF GAMMA-RAYS ON DNA FROM T3 BACTERIOPHAGE

Abstract

DNA from T3 bacteriophago was irradiated at a concentration of 30 ug/ml in dilute saline citrate solvent (Na' 0.0l95M). Molecular weight of irradiated DNA was derived from the value of its intrinsic viscosity, and was also calculated from the lowering of its melting temperature, dTm. At a dose of 10.5 ev/p, the molecular weight derived from viscosity data was 1.78 million while that calculated from dTm was 1. 76 million. Plaque forming ability (biological Electivity) of irradiated T3 DNA, was studied and was found to decrease exponentially with increasing doses of radiation. D37, the dose at which 37% of original biological activity remained was 10.5 ev/p or 9.7 Krad, at which dose, on average DNA was split into 22 pieces. DNA which had received a dose of II.4 ev/p (close to D37) required 2.6 molecules par spheroplast to synthesize an infective cantor, which was in contrast to one moleculo per spheroplast required for undamaged DNA. This indicated existence of repair mechanisms in spheroplasts, whereby pieces of DNA were linked to form a moleculo capable of synthesizing an infective center.