Global transcriptional regulator of carbon catabolite repression (CCR) and carbon catabolite activation (CCA), which ensures optimal energy usage under diverse conditions. Interacts with either P-Ser-HPr or P-Ser-Crh, leading to the formation of a complex that binds to DNA at the catabolite-response elements (cre). Binding to DNA allows activation or repression of many different genes and operons. Homodimer. Interacts with P-Ser-HPr and P-Ser-Crh.