Elaborate transcription regulation of the Bacillus subtilis ilv‐leu operon involved in the biosynthesis of branched‐chain amino acids through global regulators of CcpA, CodY and TnrA

Summary The Bacillus subtilis ilv‐leu operon involved in the biosynthesis of branched‐chain amino acids is under negative regulation mediated by TnrA and CodY, which recognize and bind to their respective cis‐elements located upstream of the ilv‐leu promoter. This operon is known to be under CcpA‐dependent positive regulation. We have currently identified a catabolite‐responsive element (cre) for this positive regulation (bases −96 to −82; +1 is the ilv‐leu transcription initiation base) by means of DNase I‐footprinting in vitro, and deletion and base‐substitution analyses of cre. Under nitrogen‐rich growth conditions in glucose‐minimal medium supplemented with glutamine and amino acids, CcpA and CodY exerted positive and negative regulation of ilv‐leu, respectively, but TnrA did not function. Moreover, CcpA and CodY were able to function without their counteracting regulation of each other, although the CcpA‐dependent positive regulation did not overcome the CodY‐dependent negative regulation. Furthermore, under nitrogen‐limited conditions in glucose‐minimal medium with glutamate as the sole nitrogen source, CcpA and TnrA exerted positive and negative regulation, respectively, but CodY did not function. This CcpA‐dependent positive regulation occurred without the TnrA‐dependent negative regulation. However, the TnrA‐dependent negative regulation did not occur without the CcpA‐dependent positive regulation, raising the possibility that this negative regulation might decrease the CcpA‐dependent positive regulation. The physiological role of this elaborate transcription regulation of the B. subtilis ilv‐leu operon in overall metabolic regulation in this organism is discussed.