Repression in Streptomyces coelicolor

A glucose kinase (glkA) mutant of Streptomyces coelicolor A3(2) M145 was selected by the ability to grow in the presence of the nonmetabolizable glucose analog 2-deoxyglucose. In this glk4 mutant, carbon catabolite repression of glycerol kinase and agarase was relieved on several carbon sources tested, even though most of these carbon sources are not metabolized via glucose kinase. This suggests that catabolite repression is not regulated by the flux through glucose kinase and that the protein itself has a regulatory role in carbon catabolite repression. A 10-fold overproduction of glucose kinase also results in relief of catabolite repression, suggesting that excess glucose kinase can titrate the repressing signal away. This could be achieved directly by competition of excess glucose kinase with its repressing form for binding sites on DNA promoter regions or indirectly by competition for binding of another regulatory protein.