A CUC triplet confers leucine-dependent regulation of the Bacillus subtilis ilv-leu operon.

Regulation of the ilv-leu operon probably involves interaction of a tR NA(GAG) with leader region mRNA. Conversion of a CUC (Leu) triplet located within the leader region to UUC (Phe), CGC (Arg), or UAC (Tyr) converted reporter gene expression to control by corresponding amino acids. Conversion of the CUC triplet to CUU (Leu) decreased expression and disrupted regulation. The results suggested that other tRNAs can substitute for tRNA(Leu) but that interactions in addition to pairing of the anticodon with the CUC triplet are important for proper control.     

Role of CodY in regulation of the Bacillus subtilis hut operon.

Bacillus subtilis mutants deficient in amino acid repression of the histidine utilization (hut) operon were isolated by transposon mutagenesis. Genetic characterization of these mutants indicated that they most likely contained transposon insertions within the codVWXY operon. The codY gene is required for nutritional regulation of the dipeptide permease (dpp) operon. An examination of hut expression in a delta codY mutant demonstrated that amino acid repression exerted at the hutOA operator, which lies immediately downstream of the hut promoter, was defective in a delta codY mutant. The codY gene product was not required for amino acid regulation of either hut induction or the expression of proline oxidase, the first enzyme in proline degradation. This indicates that more than one mechanism of amino acid repression is present in B. subtilis. An examination of dpp and hut expression in cells during exponential growth in various media revealed that the level of CodY-dependent regulation appeared to be related to the growth rate of the culture.     

The Bacillus subtilis ureABC operon.

The Bacillus subtilis ureABC operon encodes homologs of the three subunits of urease enzymes of the family Enterobacteriaceae. Disruption of ureC prevented utilization of urea as a nitrogen source and resulted in a partial growth defect in minimal medium containing limiting amounts of arginine or allantoin as the sole nitrogen source.     

Insufficient expression of the ilv-leu operon encoding enzymes of branched-chain amino acid biosynthesis limits growth of a Bacillus subtilis ccpA mutant

Bacillus subtilis ccpA mutant strains exhibit two distinct phenotypes: they are defective in catabolite repression, and their growth on minimal media is strongly impaired. This growth defect is largely due to a lack of expression of the gltAB operon. However, growth is impaired even in the presence of glutamate. Here, we demonstrate that the ccpA mutant strain needs methionine and the branched-chain amino acids for optimal growth. The control of expression of the ilv-leu operon by CcpA provides a novel regulatory link between carbon and amino acid metabolism.