THE ARGININE OPERON OF BACILLUS-STEAROTHERMOPHILUS - CHARACTERIZATIONOF THE CONTROL REGION AND ITS INTERACTION WITH THE HETEROLOGOUS BACILLUS-SUBTILIS ARGININE REPRESSOR

Mechanisms of gene regulation have not yet been extensively studied in thermophilic bacteria. In previous studies we showed that the Bacillu s stearothermophilus argCJBD gene cluster is subject to specific repre ssion by arginine. Here we report the cloning by colony hybridization, and characterization of the proximal part of the argC gene together w ith the adjacent control region of the cluster. The promoter was ident ified by primer extension mapping of the argC transcription startpoint : a sequence overlapping: it was found to be similar to the arginine o perators of B. subtilis and to a smaller extent of E. coli. Use of an argC-lacZ gene fusion revealed that the argC promoter is strongly repr essed by the heterologous B. subtilis arginine repressor/activator Ahr C in E. coli cells. Mobility shift and DNase I footprinting experiment s revealed tight, specific and arginine-dependent binding of this oper ator-like sequence to purified AhrC. It is therefore very likely that in B. stearothermophilus the expression of the argCJBD operon is modul ated by a repressor that is the thermophilic homologue of AhrC.