Cyclic AMP-independent catabolite repression in bacteria.

Until recently, only one mechanism of catabolite repression in bacteria, a mechanism dependent on the cyclic AMP receptor protein of Escherichia coli, was understood in molecular detail. Two cyclic AMP-independent catabolite repression mechanisms are currently under study. One such mechanism, found in E. coli, involves the catabolite repressor/activator (Cra) protein (formerly designated the fructose repressor FruR) which represses sugar catabolic systems and activates sugar anabolic systems. When catabolites bind to Cra, Cra dissociates from the DNA causing catabolite activation and catabolite repression, respectively. The second such mechanism, found in Bacillus subtilis, involves a catabolite-activated, ATP-dependent protein kinase that phosphorylates a specific seryl residue in the small phosphocarrier protein, HPr, of the phosphotransferase system. HPr(ser-P) binds to a transcription factor, CcpA, to promote DNA binding. DNA binding of the complex in turn promotes catabolite repression or catabolite activation, depending on the target operon. The characterization of these novel mechanisms establishes that cyclic AMP-independent catabolite control is operative in bacteria, and that multiple mechanisms of catabolite control evolved independently of each other.