The influence of amino acid starvation on the UV reversibility of the strains ofEscherichia coli B/rthy − trp − Hcr + andEscherichia coli B/rthy − trp − Hcr −

Abstract

The fraction of inducedtrp+ reversions in the strains ofEscherichia coli B/rthy−trp−Hcr+ andEscherichia coli B/rthy−trp−Hcr− was studied in the course of starvation for an essential amino acid. UV light as a mutagenic factor was used. It was found that there is a decrease in the proportion of inducedtrp+ reversions in the strain ofHcr+ type during starvation. Such a decrease was however observed only with that fraction oftrp+ reversions which is expressed in selective plates where several divisions of irradiated cells are caused. The proportion oftrp+ reversions expressed on minimal plates does not change during starvation. With the strain ofHcr− type the proportion of inducedtrp+ mutations remains unaltered irrespective of the nature of the selective plates.