Application of the tryptophanase promoter to high expression of the tryptophan synthase gene in Escherichia coli.

The application of an inducible regulation system using the tryptophanase operon promoter (TPase promoter; Ptna) was examined for its high expression of the tryptophan synthase (TS) gene in Escherichia coli. The main problem in the application of Ptna for industrial purposes is catabolite repression by glucose, since glucose is the most abundant carbon source. However, this problem could be avoided by changing glucose to an organic acid, such as succinate, fumarate, malate and acetate, in the course of cultivation after glucose initially added was completely consumed. Under these conditions, L-tryptophan was also used to induce tryptophan synthase. Thus, the specific activity of TS in E. coli strain no. 168 harbouring pBR322F-Ptna TS was increased 500-fold compared to that of the cultured host strain. About 1 mol L-tryptophan/l reaction mixture was formed from indole and L-serine at 37 degrees C for 3.5 h.