Expression of the gapA gene encoding glyceraldehyde-3-phosphate dehydrogenase of Corynebacterium glutamicum is regulated by the global regulator SugR

Regulation of expression of the gapA gene encoding glyceraldehyde-3-phosphate dehydrogenase essential for glycolysis in Corynebacterium glutamicum was studied. We applied DNA affinity beads to isolate proteins binding to the promoter region of the gapA gene and obtained SugR, which has been shown to be a repressor of pts genes involved in sugar transport system. The results of electrophoretic mobility shift assays revealed that SugR specifically bound to the gapA promoter and the consensus sequence TGTTTG in the promoter region was required for its binding. We examined expression of the gapA gene in a sugR deletion mutant. Effect of mutation in the SugR binding site on gapA-lacZ fusion expression was also examined. These assays revealed that SugR acts as a negative transcriptional regulator of the gapA gene in the absence of sugar, and repression by SugR is alleviated in the presence of sugar, i.e., fructose and sucrose. Fructose-1-phosphate and fructose-1,6-bisphosphate revealed negative effects on binding of SugR to the gapA promoter, indicating that the sugar metabolites are involved in the derepression of gapA expression.