EXPRESSION OF THE BACILLUS-SUBTILIS GABP GENE IS REGULATED INDEPENDENTLY IN RESPONSE TO NITROGEN AND AMINO-ACID AVAILABILITY

Expression from the Bacillus subtilis nrg-21 locus increases 26-fold d uring nitrogen-limited growth. The DNA corresponding to this locus was cloned and sequenced. The nucleotide sequence revealed a gene that co uld encode a protein with sequence similarity to the Escherichia coil gamma-aminobutyric acid (GABA) permease. A transposon insertion in thi s locus eliminated the uptake of GABA and severely inhibited the utili zation of GABA as a nitrogen source. Primer extension analysis reveale d that the B. subtilis gabP gene was transcribed from two overlapping promoters. Transcription from the P1 promoter was repressed during gro wth in the presence of amino acids. The product of the codY gene prove d to be required for this repression. Transcription from the P2 promot er increased during nitrogen-limited growth and was dependent upon the product of the tnrA gene. Deletion analysis revealed that activation of the P2 promoter during nitrogen-limited growth requires a nucleotid e sequence located upstream of its -35 region. Regulation of gabP expr ession by the CodY and TnrA regulatory systems, which respond to diffe rent physiological signals, allows for a wide range of gabP expression during growth on various nitrogen sources.