EXPRESSION OF THE ROCDEF OPERON INVOLVED IN ARGININE CATABOLISM IN BACILLUS-SUBTILIS

Three genes called rocD, rocE and rocF were found near the rocR gene i n B. subtilis. The product of rocD is similar to eukaryotic ornithine aminotransferases. The product of rocE shares similarity with the prod uct of B. subtilis rocC and with the product of E. coli lysP. The rocE gene may encode an arginine permease. The rocF gene encodes a polypep tide similar to several arginases. Heterologous expression in E. coli indicated that rocD encodes an ornithine aminotransferase and that roc F encodes an arginase. Arginine utilization was abolished in both rocD and rocF mutants of B. subtilis confirming the role of these genes in arginine catabolism. The rocDEF genes form an operon transcribed from a -12, -24 promoter almost identical to the -12, -24 promoter of the rocABC operon. The expression of the rocDEF operon was induced by the presence of arginine, ornithine or proline in the growth medium and de pended on the presence of the sigma factor SigL. Transcription of this operon was also abolished in a B. subtilis strain containing a null m utation in the regulatory gene rocR. Two tandemly repeated upstream ac tivating sequences very similar to those previously identified in the rocABC system were found centered at positions -120 and -70, respectiv ely, upstream from the transcription start site of rocDEF. Deletion an alysis showed that at least one upstream activating sequence is involv ed in the expression of the rocDEF operon. These sequences are probabl y the target of RocR. Analysis of a rocR'-'lacZ fusion strain showed t hat the expression of rocR is not induced by arginine and is negativel y autoregulated.