FIG. 6.

Effect of cytoplasmic glucose on the activity of MalQ and on glycogen-dependent endogenous induction. Shown is the pathway of glycogen degradation producing maltotriose, the inducer of MalT, the transcriptional activator of all mal genes. Glucosyl residues are indicated by small circles, horizontal lines between the circles indicate α(1-4) linkages, bent arrows indicate α(1-6) linkages. Unlinked arrows indicate the reducing end of the maltodextrins and glucose. Solid circles indicate the origin of maltotriose from glycogen and its further metabolism. (Lower left branch) In a glk mutant, glucose formed by the action of MalQ or by hydrolysis of glucose containing substrates (not shown) inhibit MalQ, preventing the removal of maltotriose, thus establishing high endogenous induction. (Lower right branch) Overexpression of Glk removes free glucose, allowing high MalQ activity. This leads to the removal of maltotriose by the formation of larger maltodextrins, thus causing the loss of MalT activation and a reduction in mal gene expression. Not shown here is the action of MalZ or the synthesis of glycogen.