DnrI of Streptomyces peucetius binds to the resistance genes, drrAB and drrC but is activated by daunorubicin.

The master regulator, DnrI of Streptomyces peucetius is a member of the family of transcriptional activator, Streptomyces antibiotic regulatory proteins (SARP), which controls the biosynthesis of antitumor anthracycline, daunorubicin (DNR) and doxorubicin (DXR). The binding of DnrI to the heptameric repeat sequence found within the -35 promoter region of biosynthetic gene, dpsE activates it. To combat the increased level of intracellular DNR, the cell has developed self resistance mechanism mediated by drrAB and drrC genes which are regulated by regulatory genes. We find that a drug non-producing mutant, ΔdpsA, showed sensitive phenotype in plate assay along with an increased level of dnrI transcript. Whereas the mutant grown in the presence of DNR showed a resistant phenotype with a six and eight folds increase in drrAB and drrC transcripts respectively. Computational studies followed by molecular docking showed that DnrI bound as a monomer to a slightly modified heptameric DNA motif, 5'-ACACGCA in drrA and 5'-ACAACCT in drrC which was also proved by electrophoretic mobility shift assay. These findings confirm that DnrI belongs to winged helix-turn-helix DNA-binding protein with Tetratricopeptide Repeat domain. The transcriptional regulator DnrI binds to the resistance genes at specific sites but they are activated only when an increased load of intracellular DNR is sensed.