TNRA, A TRANSCRIPTION FACTOR REQUIRED FOR GLOBAL NITROGEN REGULATION IN BACILLUS-SUBTILIS

Expression of the Bacillus subtilis nrgAB operon is derepressed during nitrogen-limited growth, We have identified a gene, tnrA, that is req uired for the activation of nrgAB expression under these growth condit ions. Analysis of the DNA sequence of the tnrA gene revealed that it e ncodes a protein with sequence similarity to GlnR, the repressor of th e B. subtilis glutamine synthetase operon, The tnrA mutant has a pleio tropic phenotype, Compared with wild-type cells, the tnrA mutant is im paired in its ability to utilize allantoin, gamma-aminobutyrate, isole ucine, nitrate, urea, and valine as nitrogen sources. During nitrogen- limited growth, transcription of the nrgAB, nasB, gabP, and ure genes is significantly reduced in the tnrA mutant compared with the levels s een in wild-type cells, In contrast, the level of glnRA expression is 4-fold higher in the tnrA mutant than in wild-type cells during nitrog en restriction. The phenotype of the tnrA mutant indicates that a glob al nitrogen regulatory system is present in B. subtilis and that this system is distinct from the Ntr regulatory system found in enteric bac teria.