NEGATIVE REGULATION OF L-ARABINOSE METABOLISM IN BACILLUS-SUBTILIS - CHARACTERIZATION OF THE ARAR (ARAC) GENE

The Bacillus subtilis araC locus, mapped at about 294 degrees on the g enetic map, was defined by mutations conferring an Ara(-) phenotype to strains bearing the metabolic araA, araB, and araD wild-type alleles (located at about 256 degrees on the genetic map) and by mutants showi ng constitutive expression of the three genes. In previous work, it ha s been postulated that the gene in which these mutations lie exerts it s effect on the ara metabolic operon in trans, and this locus was name d araC by analogy to the Escherichia coli regulatory gene. Here, we re port the cloning and sequencing of the araC locus. This region compris es two open reading frames with divergently arranged promoters, the re gulatory gene, araC, encoding a 41-kDa polypeptide, and a partially cl oned gene, termed araE, which most probably codes for a permease invol ved in the transport of L-arabinose. The DNA sequence of araC revealed that its putative product is very similar to a number of bacterial ne gative regulators (the GalR-LacI family). However, a helix-turn-helix motif was identified in the N-terminal region by its identity to the c onsensus signature sequence of another group of repressors, the GntR f amily. The lack of similarity between the predicted primary structure of the product encoded by the B. subtilis regulatory gene and the AraC regulator from E. coli and the apparently different modes of action o f these two proteins lead us to propose a new name, araR, for this gen e. The araR gene is monocistronic, and the promoter region contains -1 0 and -35 regions (as determined by primer extension analysis) similar to those recognized by RNA polymerase containing the major vegetative cell sigma factor sigma(A). An insertion-deletion mutation in the ara R gene leads to constitutive expression of the L-arabinose metabolic o peron. We demonstrate that the araR gene codes for a negative regulato r of the am operon and that the expression of araR is repressed by its own product.