Characterization of genetic coding changes in bacteria produced by ionizing radiation and by the radioactive decay of incorporated 3 H-labelled compounds.

Abstract

SummaryThe mutagen specificity of ionizing radiation from 60Co γ-rays and radioactive decay was examined, using tritium-labelled nucleic acid and protein precursors (3H-methyl-thymidine; 3H-6-uracil and 3H-histidine). Specificity was determined through an examination of bacterial revertants, using a bacterium containing a nonsense mutation in a gene for arginine biosynthesis. By using nonsense mutants of T4 as indicators, arginine revertants may be divided into classes. The presumed amino-acid insertions for classes were assigned earlier. The base changes leading to the production of revertants in particular classes were derived from amino-acid insertions, using the genetic code and knowledge that nonsense suppressors arise by single base alterations in the DNA information specifying certain tRNA anticodons. The mutagenic agents studied were not specific; rather a broad spectrum of base changes was observed. For the tritium-labelled compounds used, percentage distributions of base changes are similar to t...