This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bollon, A. P. Articles by Magee, P. T. Search for Related Content PubMed PubMed Citation Articles by Bollon, A. P. Articles by Magee, P. T.

Involvement of Threonine Deaminase in Repression of the Isoleucine-Valine and Leucine Pathways in Saccharomyces cerevisiae

^a Department of Microbiology, Yale School of Medicine, New Haven, Connecticut 06510

ABSTRACT

L-Threonine deaminase (L-threonine dehydratase [deaminating], EC 4.2.2.16) has been shown to be involved in the regulation of three of the enzymes of isoleucine-valine biosynthesis in yeast. Mutations affecting the affinity of the enzyme for isoleucine also affected the repression of acetohydroxyacid synthase, dihydroxyacid dehydrase, and reductoisomerase. The data indicate that isoleucine must be bound for effective repression of these enzymes to take place. In a strain with a nonsense mutation midway in liv 1, the gene for threonine deaminase, starvation for isoleucine or valine did not lead to derepression of the three enzymes; starvation for leucine did. The effect of the nonsense mutation is recessive; it is tentatively concluded, therefore, that intact threonine deaminase is required for derepression by two of the effectors for multivalent repression, but not by the third. A model is presented which proposes that a regulatory species of leu tRNA^leu is the key intermediate for repression and that threonine deaminase is a positive element, regulating the available pool of charged leu tRNA by binding it.

¹ Present address: Department of Biochemistry, The University of Texas Southwestern Medical School at Dallas, Dallas, Tex. 75235.

This article has been cited by other articles:

• Goldberger, R. F. (1974). Autogenous Regulation of Gene Expression: The mechanism by which a protein directly controls expression of its own structural gene is described. Science 183: 810-816 [Abstract]