SrrB, a Pseudo-Receptor Protein, Acts as a Negative Regulator for Lankacidin and Lankamycin Production in .

7434AN4, a producer of lankacidin (LC) and lankamycin (LM), carries many regulatory genes including a biosynthesis gene for signaling molecules SRBs (), an SRB receptor gene (), and a SARP ( antibiotic regulatory protein) family activator gene (). Our previous study revealed that the main regulatory cascade goes from through to , leading to LC production, whereas further regulates a second SARP gene to synthesize LM. In this study we extensively investigated the function of , a pseudo-receptor gene, by analyzing antibiotic production and transcription. Metabolite analysis showed that the mutation increased both LC and LM production over four-folds. Transcription, gel shift, and DNase I footprinting experiments revealed that and are expressed under the SRB/SrrA regulatory system, and at the later stage, SrrB represses expression by binding to the promoter region of . These findings confirmed that SrrB acts as a negative regulator of the activator gene to control LC and LM production at the later stage of fermentation in .