MUTATIONS THAT RELIEVE NUTRITIONAL REPRESSION OF THE BACILLUS-SUBTILIS DIPEPTIDE PERMEASE OPERON

The Bacillus subtilis dciA operon encodes a dipeptide transport comple x that is induced rapidly as cells enter stationary phase and initiate sporulation. Expression of this operon in growing cells is repressed by glucose, by a mixture of amino acids, and by the AbrB protein. A ge netic screen was devised to identify mutations that allow inappropriat e expression from the dciA promoter during growth. These mutations res ulted in increased dciA transcription during growth in nutrient broth, in minimal amino acids medium, and in minimal glucose medium. Some of the mutations, called dcs (dciA control site), were cloned and shown by sequence analysis to cluster near the start site of dciA transcript ion. Primer extension and in vitro transcription analysis revealed tha t the dcs mutations did not create a new promoter. These mutations may therefore disrupt an operator site necessary for the binding of a neg ative regulator responsive to the nutritional state of the cell. The d cs mutant promoters were still subject to AbrB control, suggesting tha t the dciA operon is regulated by at least two proteins, AbrB and a nu tritionally responsive regulator. The gene(s) for the putative nutriti onal regulator may be defined by the cod (control of dciA) mutations, which appeared to relieve amino acid and glucose repression of dciA by altering a diffusible factor. An abrB cod double mutant exhibited hig h-level expression of dciA during exponential growth phase.