Cloning and characterization of the glnA gene of Azospirillum brasilense Sp7.

A plasmid which, by complementation, restored a Gln+Nif+ phenotype to the Gln-Nif- Azospirillum brasilense mutant 7029, was isolated from a gene bank of total DNA of A. brasilense Sp7 (ATCC 29145) constructed in the broad host range vector pVK100. This plasmid contained the structural gene (glnA) for glutamine synthetase. The glnA gene was mapped by Tn5 insertion and DNA hybridization with a Klebsiella pneumoniae glnA probe. The direction of transcription of glnA was determined. The glnA product was identified as a 50-Kd polypeptide which could be adenylylated in Escherichia coli, and glutamine synthetase activity was characterized in E. coli. Plasmids containing the glnA gene restored glutamine-independent growth and a Nif+ phenotype to Gln-Nif- and Gln-Nifc mutants of Azospirillum.