| Saccharopolyspora erythraea produces erythromycin, an antibiotic important in human medicine. Actinomycetes similar to S. erythraea produce nearly two-thirds of bioactive molecules synthesized by microorganisms, including antibiotics, antitumor agents, and immunosuppressants. The synthesis of these molecules often coincides with complex morphological changes during the life cycle of a bacterium. Consistent with that long-standing observation, our laboratory recently isolated from Saccharopolyspora erythraea a regulator of the biosynthetic genes of erythromycin (EryR) that closely resembles a key developmental protein (BldD) of Streptomyces coelicolor, a well-studied actinomycete. This work describes (1) genetic properties of the protein, EryR, (2) biochemical properties of EryR binding DNA, (3) structural, genetic, and biochemical similarities between EryR and its ortholog BldD, and (4) improvement in antibiotic titers produced by an actinomycete.; We show that EryR links the synthesis of erythromycin to morphological changes caused by impending starvation. A deletion of eryR from S. erythraea decreases erythromycin production by 6-fold, and prevents bacterial colonies from sporulating. S. erythraea also produces an abundant protein in the presence of EryR; orthologs of this protein, EshA, in other bacterial species participate in sporulation and the synthesis of antibiotics.; Moreover, we demonstrate that EryR and BldD are structurally and functionally similar. Like BldD, EryR requires a tyrosine residue (Y61) for structural integrity, binds its own promoter, and represses its own transcription. Mutagenesis of DNA sites bound by EryR revealed a consensus sequence of TCACt (n) m TCAcC, resembling the consensus sequence of BldD. EryR and BldD bind their promoters with similar dissociation constants. (In contrast, EryR binds promoters in the biosynthetic cluster of erythromycin an order of magnitude less strongly.) EryR binds promoters of several sigma factors of S. erythraea, SigH, WhiG, and BldN, whose orthologs BldD binds in S. coelicolor. Furthermore, eryR complements a deletion of bldD in S. coelicolor, restoring sporulation and the synthesis of antibiotics. Overexpression of eryR in S. coelicolor also increased titers of actinorhodin and undecylprodigiosin by 30% and 70%, respectively. Together these results identify the first member of the BldD family that directly regulates biosynthetic genes of an antibiotic and demonstrate multiple roles for EryR in S. erythraea. |
