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J Bacteriol. 1972 January; 109(1): 315-325
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Growth-Linked Instability of a Mutant Valyl-Transfer Ribonucleic Acid Synthetase in Escherichia coli¹

^a Department of Biological Sciences, Purdue University, Lafayette, Indiana 47907

ABSTRACT

The valyl-transfer ribonucleic acid (tRNA) synthetase of Escherichia coli strain NP2907, previously described as having an elevated K_m for adenosine triphosphate and reduced stability in vitro compared to the wild type, was found to be conditionally thermolabile in vivo. The rate of inactivation of this enzyme at a particular temperature appears to be coordinated with the rate of growth; at 40 C this coordination results in equal rates of synthesis and destruction over a wide range of growth rates. In vitro studies showed that conditions favoring maintenance of the valyl-tRNA synthetase-valyl adenylate complex conferred complete protection against inactivation at 40 C, whereas the further addition of uncharged tRNA caused rapid, irreversible decay. We propose that the rate of inactivation of this mutant valyl-tRNA synthetase in vivo is a function of the ratio of deacylated to acylated tRNA^val and that this ratio is a function of growth rate. The event which renders the valyl-tRNA synthetase susceptible to inactivation is likely to be the normal breakdown of the valyl-tRNA synthetase–valyl-adenylate complex during a cycle of aminoacylation of tRNA^val.

² Present address: Department of Biological Sciences, Dartmouth College, Hanover, N.H. 03755.

³ Present address: Department of Microbiology, The University of Michigan, Ann Arbor, Mich. 48104.

¹ The studies reported here are taken from a thesis submitted by James J. Anderson to Purdue University in partial fulfillment of the requirements for the Ph.D. degree. A preliminary report of some of these findings has appeared (14).

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