A Comparison of the Direct Effect of γ-Rays on Escherichia coli Ribosomes and Bacteriophage f2

Abstract

γ-Ray inactivation of the ability of Escherichia coli MRE 600 ribosomes to support polyuridylic acid-directed polymerization of phenylalanine was compared with the inactivation of the reproductive capacity of bacteriophage f2. In lyophilized preparations of the mixture of the two ribonucleoproteins (irradiated at +20°C), both components were four to five times more radiosensitive than when fully protected. The full protection of ribosomes, resulting in a ${\rm D}_{37}$ of 2.2 MR, was obtained when a suspension or a lyophilized preparation was irradiated at -80°C or when oxidized glutathione was present in lyophilized preparations irradiated at +20°C. A combination of the two treatments did not result in a further increase in radioresistance. Bacteriophage f2 irradiated at -80°C was not fully protected, and the addition of high concentrations of oxidized glutathione or Bacto-Tryptone was needed to reach maximum protection and a ${\rm D}_{37}$ of 1 MR. At full prote...