ULTRAVIOLET LIGHT-INDUCED MUTATION AND DEOXYRIBONUCLEIC ACID SYNTHESIS IN ESCHERICHIA COLI

Abstract

An arginine-requiring mutant of the thymine-requiring strain Escherichia coli 15T- was examined for susceptibility to induction by ultraviolet light (UV) of mutation to arginine independence in the presence or absence of deoxyribonucleic acid (DNA) synthesis, as regulated by presence or absence of thymine. The frequency of mutations remained constant during thymine starvation and upon subsequent thymine supplementation despite a two-fold increase in sensitivity to the lethal action of UV during starvation. A post-irradiation period of lability in which the mutagenic process is dependent upon a general supplement of a mixture of amino acids was found to be extended by thymine starvation and to be terminated upon thymine supplementation. Thus the definitive fixa- tion of the mutation depends upon DNA synthesis. The rate and extent of the loss of potential mutants which occurs upon post-irradiation deprivation of the general amino acid supplement was indifferent to the presence or absence of thymine and thus apparently occurs independently of DNA synthesis.