Stress-response sigma factor sigma(H) directs expression of the gltB gene encoding glutamate synthase in Streptomyces coelicolor A3(2).

Using the previously established Escherichia coli two-plasmid system, we identified a promoter recognized by the Streptomyces coelicolor stress-response sigma factor sigma(H). The promoter directed expression of the gltB gene, encoding a protein with considerable homology with large subunit of glutamate synthases. S1-nuclease mapping using RNA prepared from S. coelicolor identified an identical transcription start point corresponding to the promoter. The level of the transcript from this promoter was substantially reduced in a S. coelicolor sigH mutant. In addition to this sigH-dependent gltBp2 promoter, expression of the S. coelicolor gltB gene was directed by two other promoters, gltBp1 and gltBp3, independent upon sigH. S. coelicolor core RNA polymerase, after complementation with sigma(H), was able to recognize the gltBp2 promoter in vitro. These results suggested that the S. coelicolor gltB gene is under the control of stress-response sigma(H).