Cloning and preliminary characterization of the sacS locus from Bacillus subtilis which controls the regulation of the exoenzyme levansucrase.

The regulation of sacB, the gene encoding Bacillus subtilis levansucrase is altered by mutations located in several loci unlinked to sacB. Amongst these, the sacS locus seems to play an important role in the induction of sacB by sucrose. We have cloned sacS and found evidence suggesting that it contains two genes. The product of the first gene might repress the expression of the second; the second gene encodes a positive regulator of levansucrase synthesis, since its deletion abolishes this synthesis. There is a palindromic sequence resembling Q-independent terminators between the sacB promoter and the structural gene. Mutations affecting this palindrome make sacB constitutive. This suggests that the putative terminator is involved in the induction of sacB by sucrose. We discuss the possibility that the sacS-encoded positive regulator is a sucrose-dependent antiterminator which modulates transcription termination between the sacB promoter and the structural gene.