An unusual condition of leucine transfer RNA appearing during leucine starvation of Escherichia coli

Abstract

Contrary to expectation, starvation of Escherichia coli for any one of several required amino acids does not lead to complete deacylation of the affined tRNA molecules. In particular, during leucine starvation, some of the leucine tRNA remains acylated with leucine. In leucine-starved RC str † † Abbreviations used: RC str and RC rel, the phenotypes representing stringent and relaxed control of RNA synthesis; standard abbreviations for amino acids and vitamins; MAK, methylated albumin kieselguhr. strains, furthermore, some of the leucine tRNA carries a protector against destruction by periodate oxidation. This protector is not removed by mild alkali treatment, but is removed by a partially purified aminoacyl-tRNA synthetase enzyme preparation in the absence of AMP and pyrophosphate. Hence the protector is neither leucine nor one of the standard amino acids. The leucine tRNA of leucine-starved RC rel strains does not carry this protector, nor is the protector present on the leucine tRNA of exponentially growing bacteria. Only one of the several species of leucine tRNA carries the protector, suggesting that this species may fulfill a regulatory function.