redD and actII-ORF4, Pathway-Specific Regulatory Genes for Antibiotic Production in Streptomyces coelicolor A3(2), Are Transcribed In Vitro by an RNA Polymerase Holoenzyme Containing σhrdD

redD and actII-ORF4, regulatory genes required for synthesis of the antibiotics undecylprodigiosin and actinorhodin by Streptomyces coelicolor A3(2), were transcribed in vitro by an RNA polymerase holoenzyme containing σhrdD. Disruption of hrdD had no effect on antibiotic production, indicating that redD and actII-ORF4 are transcribed in vivo by at least one other RNA polymerase holoenzyme. These data provide the first experimental evidence that HrdD can function as a σ factor.