Regulation of Tyrosine and Phenylalanine Biosynthesis in Escherichia coli K-12: Properties of the tyrR Gene Product

Abstract

A spontaneous amber tyrR mutant has been isolated in which constitutive synthesis of 3-deoxy- d -arabinoheptulosonic acid 7-phosphate (DAHP) synthetase (tyr) and DAHP synthetase (phe) is suppressible by supC − , supD − , supF − and supU − . This finding suggests the tyrR gene product is a protein. Derepression of DAHP synthetase (phe) in this and in seven other spontaneous tyrR mutants and in four Mu-1-induced tyrR mutants provides further evidence for the involvement of the tyrR gene product in phenylalanine biosynthesis. Evidence that the tyrR product is a component of repressor, rather than an enzyme involved in its synthesis or modification, comes from a study of a temperature-sensitive tyrR mutant. This mutant is of the thermolabile type, since derepression occurs rapidly and in the presence and absence of growth.