Identification of two novel regulatory genes involved in pristinamycin biosynthesis and elucidation of the mechanism for AtrA-p-mediated regulation in Streptomyces pristinaespiralis

In this study, using a transposon-based strategy, two novel regulatory genes were identified as being involved in the biosynthesis of both pristinamycin I (PI) and II (PII) in Streptomyces pristinaespiralis, including a TetR-family regulatory gene atrA-p (SSDG_00466) and an orphan histidine kinase gene SSDG_02492. The mechanism by which AtrA-p exerted a positive role in pristinamycin production was elucidated. We showed that deletion of atrA-p resulted in a delayed production of both PI and PII as well as reduced PII production. Transcriptional analysis integrated with electrophoretic mobility shift assays (EMSAs) demonstrated that AtrA-p played a positive role in pristinamycin production by directly activating the transcription of two cluster-situated regulatory genes, spbR and papR5, which encode a γ-butyrolactone receptor protein and a TetR-family repressor, respectively. The precise AtrA-p-binding sites upstream of these two targets were determined, which allowed the identification of a relatively conserved binding motif comprising two 5-nt inverted repeats separated by a variable 5-nt sequence (5′-GGAAT-n₅-ATTCC-3′) possibly required for the regulation of AtrA-like regulators in Streptomyces. Base substitutions of the AtrA-p-binding sites on the genome caused similar decreases in spbR and papR5 transcription as those observed in ∆atrA-p. Taken together, herein, a novel mechanism for AtrA-dependent regulation of antibiotic biosynthesis was revealed in S. pristinaespiralis, which is distinct from those of its homologs, AtrA-c from Streptomyces coelicolor, AtrA-g from Streptomyces griseus, and AtrA from Streptomyces roseosporus that perform their effects in antibiotic biosynthesis directly via pathway-specific activator genes or the biosynthetic structural genes.