Figure 8.

A plausible model for the roles of SabR1 and its ligands (SABs) in regulation of nikkomycin biosynthesis. Signal molecules SABs synthesized by sab exert regulatory functions via the cognate receptor SabR1. SabR1 can repress the transcription of cprC and other target genes (sabR1, sabR2, and sabA). CprC is a new activator of adpA, and AdpA positively regulates nikkomycin production by activating the cluster-situated regulatory gene sanG. In WT strain, binding of SABs to SabR1 causes the dissociation of SabR1 from cprC promoter and increases crpC transcription, which in turn activates adpA transcription to trigger nikkomycin biosynthesis. When sabA is disrupted or SABs are absent, binding of SabR1 to cprC would result in the repression of cprC and consequently cause the transcriptional reduction of adpA and nikkomycin biosynthetic genes.