Regulation of glutamine synthetase in Streptomyces coelicolor

Glutamine synthetase (GS) in Streptomyces coelicolor was shown to be regulated at two levels. First, the S. coelicolor GS protein is subject to a posttranslational covalent modification which is likely to involve adenylylation. Adenylylation is important in regulating GS activity both after sudden changes in ammonium availability and during steady-state growth. Since higher levels of adenylylated GS were seen in S. coelicolor mutants deficient in glutamate synthase than in wild-type cells, glutamine or a metabolite derived from glutamine is likely to be involved in the metabolic signal that regulates GS adenylylation. Second, the GS structural gene (glnA) is transcriptionally regulated in response to nitrogen availability during steady-state growth. Transcription of the glnA gene occurred from the same promoter during vegetative growth, stationary phase, and sporulation. The nucleotide sequence of this promoter has significant homology with the -10, but not the -35, region of the consensus sequence of Streptomyces vegetative promoters. The glnA gene is transcribed as a monocistronic mRNA.