Abstract

Maintenance of a mini-F recombinant plasmid in E. coli and expression of its tryptophan synthase genes. Process Biochem. 22: 165-168. 1987. H. Yukawa, Y. Kurusu, M. Shimazu, H. Yamagata and M. Terasawa.

The maintenance of a recombinant plasmid in E. coli and the expression of tryptophan synthase (TS) genes were examined by the use of the mini-F plasmid, pBR322-trpBA. The inserted mini-F fragment conferred stable inheritance on this plasmid with high copy number. In this study E. coli K-12 strain (wild type) was usable as a host because the transformant of this strain could grow satisfactorily and maintain the plasmid stably. 3-Indole acrylic acid (IA) was added to the culture medium in order to release partially the repression of gene expression from the trp promoter. The addition of IA in the middle of the logarithmic phase of cultivation was effective in avoiding the inhibition of bacterial growth by IA itself and also led to higher expression of TS. The enzymeic formation of L-tryptophan from indole and L-serin was examined: about one mole of tryptophan was formed in a litre of reaction mixture at 37°C after 31/2 hours.

---