Tandem promoters, tsrp1 and tsrp2, direct transcription of the thiostrepton resistance gene (tsr) of Streptomyces azureus: transcriptional initiation from tsrp2 occurs after deletion of the -35 region.

Nuclease S1 protection experiments indicated that the thiostrepton resistance gene (tsr) of Streptomyces azureus is transcribed from tandem promoters, tsrp1 and tsrp2, that initiate transcription 45 and 173 nucleotides, respectively, upstream of the presumptive translational start codon. The -10 regions of both promoters show similarity to the consensus sequence for the major class of prokaryotic promoters, but the -35 regions do not, although they show some similarity to each other. Replacement of sequences upstream of position -22 relative to the tsrp2 start site with two different DNA segments affected the levels of the tsrp2 transcript but did not alter the tsrp2 initiation site. In vitro transcription assays using RNA polymerase from Streptomyces coelicolor A3(2) also confirmed the location of tsrp2 and identified additional start sites near tsrp2 that were barely detectable with in vivo synthesised RNA. Transcripts corresponding to initiation in vitro at trsp1 could not be detected, suggesting that additional factors are required for utilisation of this promoter.