| Streptomyces have abundant secondary metabolite and there are numerous silent secondary metabolite biosynthetic gene clusters in streptomyces. Bioactive natural products synthesized by activating these cryptic gene clusters has shown to be main source of candidate drugs. Bioinformatics analysis of breeding strains Steptomyces chattanoogensis L10 revealed there were 32 silent biosynthetic gene clusters, one of them was angucycline biosynthetic gene cluster (cha). Overexpression of a pathway-specific activator gene chal successfully triggered the expression of the genes and produce chattamycins A and chattamycin B. Cell viability assays demonstrated that chattamycin B possesses a promising antitumor activities against human cancer cell lines.This study focus on another pathway-specific regulator ChaK, which is also lacated in the cha cluster and study on its mechanism deeply. Researsh showed that ChaK specifically bound to the promoter of chaJ and there were two ChaK-binding sites located in the promoter. The transcription of chaJ was shown to be negatively regulated by ChaK. In addition, when chattamycin B accumulated to a certain concentration; it can specifically modulate the DNA-binding activities of ChaK on chaJ promoter and relieve ChaK-mediated repression of chaJ. ChaK also bound to its own promoter and qRT-PCR experiment show that ChaK repress its own transcription.There are six homologous proteins of y-butyrolactone(GBL) receptors in S. chattanoogensis L10. One of GBL receptor ScgR positively regulated the synthesis of chattamycin, while the other four homologous proteins (ScgR2/ScgR3/ScgR5/SprA) down-regulated the synthesis of chattamycin. Furthermore, the last homologous protein of GBL receptors-ChaKl located in the chattamycin biosynthetic gene cluster. By comparing Transcriptional differences and chattamycin yield of the mutant strains ZJUQ2 with wild strain S.chattanoogensis L10, we found ChaKl also down-regulated the synthesis of chattamycin. |
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