Chorismate-dependent transcriptional regulation of quinate/shikimate utilization genes by LysR-type transcriptional regulator QsuR in Corynebacterium glutamicum: carbon flow control at metabolic branch point.

The qsu operon of Corynebacterium glutamicum comprises four genes (qsuABCD) that underpin the microorganism's quinate/shikimate utilization pathways. The genes encode enzymes that catalyse reactions at the metabolic branch point between the biosynthesis route for synthesis of aromatic compounds and the catabolic route for degradation of quinate and shikimate for energy production. A qsuR gene located immediately upstream of qsuA encodes a protein (QsuR) which activates the operon in the presence of quinate or shikimate. Three observations support chorismate, an intermediate of the biosynthesis route, as a direct effector of QsuR: First, induction of qsuA mRNA in the presence of either quinate or shikimate disappears upon deletion of the gene encoding chorismate synthase. Second, chorismate accumulates when the operon is induced. Third, a DNase I-protected segment by QsuR is shortened in the presence of chorismate. The QsuR tetramer senses the accumulation of chorismate and activates qsu genes that promote the quinate/shikimate catabolic instead of the aromatic compounds biosynthetic route. Such chorismate-dependent control of carbon flow has not been previously described.