In the absence of glucose, represses the transcription of the gapA operon, which encodes five key glycolytic enzymes. Binds specifically to the cggR-gapA promoter region and blocks the progression of the RNA polymerase, leading to the arrest of the transcription. Stability and function are regulated by the effector molecule fructose-1,6-bisphosphate (FBP). In the presence of glucose, binding of FBP to the low-affinity sugar-binding site of CggR disrupts dimer/dimer bridging interactions and triggers a tetramer to dimer transition, which leaves two physically independent dimers on the target DNA and allows transcription of the downstream coding sequences by the RNA polymerase. In addition, FBP and several other phosphorylated compounds can bind to a high-affinity binding-site and protect CggR against aggregation and proteolysis. Homotetramer. Binds primarily as a dimer to each half-site of the full-length operator, with much higher affinity for the right site. Then, both dimers interact, bridging the two-half sites of the operator region. Contains an N-terminal DNA-binding domain and a large C-terminal effector-binding domain. Contains two distinct sugar-binding sites with different affinities. Belongs to the SorC transcriptional regulatory family.