INDUCTION OF THE BACILLUS-SUBTILIS PTSGHI OPERON BY GLUCOSE IS CONTROLLED BY A NOVEL ANTITERMINATOR, GLCT

Glucose is the preferred carbon and energy source of Bacillus subtilis . It is transported into the cell by the glucose-specific phosphoenolp yruvate:sugar phosphotransferase system (PTS) encoded by the ptsGHI lo cus. We show here that these three genes (ptsG, ptsH, and ptsI) form a n operon, the expression of which is inducible by glucose. In addition , ptsH and ptsI form a constitutive ptsHI operon. The promoter of the ptsGHI operon was mapped and expression from this promoter was found t o be constitutive. Deletion mapping of the promoter region revealed th e presence of a transcriptional terminator as a regulatory element bet ween the promoter and coding region of the ptsG gene. Mutations within the ptsG gene were characterized and their consequences on the expres sion of ptsG studied. The results suggest that expression of the ptsGH I operon is subject to negative autoregulation by the glucose permease , which is the ptsG; gene product. A regulatory gene located upstream of the ptsGHI operon, termed glcT, was also identified. The GlcT prote in is a novel member of the BglG family of transcriptional antitermina tors and is essential for the expression of the ptsGHI operon. A delet ion of the terminator alleviates the need for GlcT. The activity of Gl cT is negatively regulated by the glucose permease.