Autoregulation: a role for a biosynthetic enzyme in the control of gene expression.

It was previously proposed, primarily on the basis of evidence in vitro, that L-threonine deaminase, the ilvA gene product, is required for repression of its own synthesis and for repression of the other genes in the ilv-ADE operon. In this communication, evidence in vivo is presented that supports this autoregulatory model. Further evidence is presented that suggests that L-threonine deaminase is also required for induction of the ilvC gene product. The autoregulatory model is presented in an expanded form to include recent evidence that L-threonine deaminase (EC 4.2.1.16) is a central element for repression of the ilvADE and ilvB operons, and for induction of the ilvC operon.