Altered regulation of the glnA gene in glutamine synthetase mutants of Bacillus subtilis

Abstract

Expression of beta-galactosidase by Bacillus subtilis strains carrying transcriptional fusions of the glnA promoter region to the Escherichia coli lacZ gene was found to be regulated by the nitrogen source in glnA+ strains. The pattern of regulation was the same as that for glutamine synthetase (GS); the strongest repression was seen when glutamine was present in the medium. To see this regulation it was necessary for the fusion to be in low copy number, a condition achieved by forcing integration into the chromosome. We constructed a strain carrying a deletion mutation (glnA200) that removes part of the 5' end of the glnA structural gene. This strain did not produce any detectable GS activity or measurable GS antigen. We introduced this mutation and other glnA mutations (glnA73, glnA93, and glnA100) into strains carrying glnA-lacZ fusions. When the strains were grown with glutamine as the nitrogen source, beta-galactosidase activity was found to be derepressed. These results indicate that functional glnA gene product is required for the regulation of transcription from the glnA promoter. This supports the conclusion of our previous studies of the B. subtilis glnA gene cloned in E. coli. Additional factors may also be involved in glnA control. In particular, our results suggest that a 500-base-pair sequence of DNA between the promoter region and the start of the glnA structural gene plays a role in regulation; strains carrying this region within the glnA-lacZ fusion and unable to produce functional GS exhibited only partially derepressed beta-galactosidase levels when grown in the presence of glutamine.