GLUCITOL INDUCTION IN BACILLUS-SUBTILIS IS MEDIATED BY A REGULATORY FACTOR, GUTR

Expression of the glucitol dehydrogenase gene (gutB) is suggested to b e regulated both positively and negatively in Bacillus subtilis. A mut ation in the gutR locus results in the constitutive expression of gutB . The exact nature of this mutation and the function of gutR are still unknown. Cloning and characterization of gutR indicated that this gen e is located immediately upstream of gutB and is transcribed in the op posite direction relative to gutB. GutR is suggested to be a 95-kDa pr otein with a putative helix-turn-helix motif and a nucleotide binding domain at the N-terminal region. At the C-terminal region, a short seq uence of GutR shows homology with two proteins, Cyc8 (glucose repressi on mediator protein) and GsiA (glucose starvation-inducible protein), known to be directly or indirectly involved in catabolite repression. Part of the C-terminal conserved sequence from these proteins shows al l the features observed in the tetratricopeptide motif found in many e ucaryotic proteins. To study the functional role of gutR, chromosomal gutR was insertionally inactivated. A total loss of glucitol inducibil ity was observed. Reintroduction of a functional gutR to the GutR-defi cient strain through integration at the amyE locus restores the induci bility. Therefore, GutR serves as a regulatory factor to modulate gluc itol induction. The nature of the gutR1 mutation was also determined. A single amino acid change (serine-289 to arginine-289) near the putat ive nucleotide binding motif B in GutR is responsible for the observed phenotype. Possible models for the action of GutR are discussed.