Transcriptional analysis of the gene for glutamine synthetase II and two upstream genes inStreptomyces coelicolorA3(2)

The glutamine synthetase II (GSII, encoded byglnII) activity detectable in crude extracts fromStreptomyces coelicoloris low compared to the activity of glutamine synthetase I (GSI, encoded byglnA) and to that of GSII fromS. viridochromogenes. We have identified and sequenced a 3.9-kbBglII-BamHI fragment carrying the glutamine synthetase II gene (glnII) fromS. coelicolor. BesidesglnII, this region contains four ORFs (orf1–orf4). While homologues oforf1andorf2were also found in theglnIIregion of theS. viridochromogeneschromosome, this was not the case fororf3andorf4, which encode a putative hydrolase and a transcriptional regulator (Ptr) of the MarR family, respectively. High-resolution S1 nuclease mapping showed that theS. coelicolor glnIIgene is expressed from two overlapping promoters. The first comprises a vegetative promoter sequence and the second contains sequence elements that are recognized by Eσ31. Similar promoter structures were found upstream of theS. viridochromogenes glnIIgene. The involvement ofptringlnIIregulation was studied by gel retardation assays. Recombinant Ptr interacted with the upstream region ofptr, but not with the promoter region ofglnII. Aptrgene replacement mutant (S. coelicolorIP) was also constructed. RT-PCR analysis of RNA from wild-typeS. coelicolorand the IP mutant demonstrated that expression oforf3depends on Ptr. Thus, the difference in gene organization betweenS. coelicolorandS. viridochromogenesis not responsible for the difference in GSII activity.