Synthesis of specific transfer ribonucleic acids during methionine starvation in Escherichia coli 113-3

Abstract

Escherichia coli mutant 113-3, derived from strain W, requires either vitamin B 12 or methionine for growth. Ribonucleic acids are synthesized without concomitant protein synthesis and cell multiplication when a culture of this mutant is incubated in the absence of methionine. The amounts of RNA and transfer RNA synthesized during methionine starvation depended on the duration of incubation. The co-ordination ratio of tRNA to total RNA indicated that synthesis of tRNA is regulated non-co-ordinately with reference to total RNA during methionine starvation. It is proposed that all classes of RNA are regulated non-co-ordinately in the absence of methionine in this strain. Reverse-phase chromatography revealed two peaks for valyl-tRNA under normal conditions, while under conditions of methionine deprivation an additional peak was found. These observations indicate the synthesis of a new species of undermethylated tRNA which is charged by valyl-tRNA synthetase. The possibility is discussed that this new undermethylated sub-species of valyl-tRNA synthesized in the absence of methionine is a “pre-tRNA”.