Feedback regulation of doxorubicin biosynthesis in Streptomyces peucetius

DnrO, one of three DNA binding regulatory proteins involved in daunorubicin biosynthesis in Streptomyces peucetius, has been purified as a maltose-binding protein–DnrO (MBP–DnrO) fusion protein. Gel mobility shift assays showed that it specifically bound to a DNA fragment containing both dnrN and dnrO promoters. In the presence of some low-molecular-weight compounds from the daunorubicin biosynthetic pathway, the DNA binding ability of MBP–DnrO was affected. Melanin production assays showed that both DnrO and DnrN were required for the increased activity of the dnrI promoter. Rhodomycin D (RHOD), one of the intermediates in the DNR and DXR biosynthetic pathways, had a positive effect on dnrI promoter activity only in the presence of both DnrO and DnrN proteins. The promoter activity of dnrO gene decreased in the presence of the DnrO protein, suggesting that dnrO gene was autoregulated. Repression could be relieved when RHOD was present in the culture, indicating that RHOD might directly interact with the DnrO protein.