Genetic evidence for a positive-acting regulatory factor mediating induction in the tryptophan pathway of Pseudomonas aeruginosa

Abstract

A series of deletions of most or all of trpA, the distal member of the Pseudomonas aeruginosa tryptophan synthase structural gene pair, was constructed by BAL31 nuclease digestion and religation of a suitable plasmid. The residual trpB gene showed normal regulation, virtually ruling out the hypothesis of autogenous regulation proposed earlier on the basis of indirect evidence. On the other hand, SacII-mediated deletion of either or both of two small segments upstream from the trpBA promoter resulted in a fixed, low level of expression of the tryptophan synthase genes. Complementation studies implicated this region as the source of a diffusable, positive-acting regulatory factor responsible for the induction of the tryptophan synthase genes by their substrate, indoleglycerol phosphate.