Correlation of Loss of Photoreversibility of Ultra-violet-induced Mutations with Deoxyribonucleic Acid Synthesis

Abstract

PREVIOUS work suggests that nucleic acid precursors altered in vivo by ultra-violet light serve as metabolic intermediates for mutation induction in Escherichia coli ¹. Other studies indicate that in the absence of an adequate source of nitrogen, an immediate and rapid decline in frequency of mutations induced by ultra-violet light occurs^2,3. Prevention of this decline depends on the availability of a complex supply of amino-acids immediately following radiation exposure. The potential mutation is modified during post-irradiation incubation so that it is no longer subject to reversal by those agents inhibitory to protein or ribonucleic acid synthesis which cause decline in mutation frequency. Progression of loss of mutation susceptibility to chloramphenicol reversal is closely correlated with the post-irradiation synthesis of ribonucleic acid. Furthermore, experimentation has shown that a relation exists between the amount of post-irradiation ribonucleic acid which has been synthesized at the time of addition of chloramphenicol, the rate of synthesis of deoxyribonucleic acid in the presence of chloramphenicol, and the induced mutation frequency response obtained at subsequent plating⁴. These results suggest that ribonucleic acid and protein syntheses are required for mutation induction and synthesis of deoxyribonucleic acid following exposure to ultra-violet light. It would appear that only those cells which have synthesized the ribonucleic acid and protein necessary for genetic replication prior to addition of chloramphenicol are able to reproduce their deoxyribonucleic acid and thereby acquire mutant characters.