Transcriptional repressor of genes encoding both fructose and glucose metabolic enzymes such as phosphofructokinase (PFK) or 2-keto-3-deoxy-D-gluconate kinase (KDGK) during growth on glycerol. Required for the glycerol-mediated repression of pfkB-specific transcripts, but not needed for the high-levels of the pfkB-specific transcript present when cells are grown on fructose. Expression is repressed by glycerol but highly up-regulated in the presence of fructose or glucose, regardless of glycerol supplementation. Leads to pfkB-specific transcript up-regulation.