Regulation of expression of the valine (branched-chain amino acid) dehydrogenase-encoding gene from Streptomyces coelicolor

Abstract

Expression of the Streptomyces coelicolor (Sc) valine (branched-chain amino acid) dehydrogenase-encoding gene (vdh) is regulated by valine, glucose and NH 4 + at the transcriptional level. The results of assays for the level of accumulated vdh mRNA in the Sc J802 strain by primer extension experiments and for the level of catechol dioxygenase (Xy1E) activity in Sc J802 (vdh::xylE) transformants show that transcription of the vdh gene is induced approx. 2.5-fold by valine, as compared to asparagine as the sole nitrogen source in the presence of glucose as carbon source. Valine induction is repressed by glucose, as compared to glycerol as the carbon source, and by NH 4 +. Glucose catabolite repression is relieved in Sc M480, a glucose kinase ( glkA) deletion mutant. This suggests that glucose repression of vdh and carbohydrate metabolism are due to the same mechanism in Sc, which involves glucose kinase.