Effect of mutations causing gluconate kinase or gluconate permease deficiency on expression of the Bacillus subtilis gnt operon

The gluconate (gnt) operon contains genes for a repressor of the operon, gluconate kinase, and gluconate permease. A nonleaky kinase mutation (gntK4) induced the gnt operon constitutively through interaction of the repressor with an inducer of gluconate which had been endogenously formed and accumulated in the cell owing to the complete deficiency of the kinase even in the absence of gluconate in the medium. In contrast, a nonleaky permease mutation (gntP9) never induced the operon by gluconate likely because it cannot give rise to its inducing concentration in the cell even in the presence of gluconate in the medium.