THE EFFECT OF THE LACY GENE ON THE INDUCTION OF IPTG INDUCIBLE PROMOTERS, STUDIED IN ESCHERICHIA-COLI AND PSEUDOMONAS-FLUORESCENS

The role of the Escherichia coli lacY gene product (the lactose permea se) in the induction of isopropyl-beta-D-thiogalactopyranoside (IPTG) inducible promoters was studied in E. coli and P. fluorescens. This wa s done by comparing strains containing a lacIPOZYA chromosomal insert with newly constructed strains containing inserts without the lacY gen e (lacIPOZ). The lactose operon inserts were introduced as single-copy chromosomal inserts to eliminate differences in expression caused by differences in copy number. Comparison between the two types of insert s showed that the lactose permease was essential to allow growth on la ctose by both bacteria and that the lactose permease plays an importan t role in transporting the inducer IPTG across the membrane of P. fluo rescens. The use of a functional lactose permease allows expression of beta-galactosidase to increase more than fivefold from a wild-type la c promoter in P. fluorescens SS1001. We suggest that an increase in th e rate of protein synthesis from lac-type promoters could be enhanced if an active lactose permease is present as well.