CATABOLITE REPRESSION OF THE BACILLUS-SUBTILIS GNT OPERON EXERTED BY 2 CATABOLITE-RESPONSIVE ELEMENTS

Catabolite repression of Bacillus subtilis catabolic operons is suppos ed to occur via a negative regulatory mechanism involving the recognit ion of a cis-acting catabolite-responsive element (cre) by a complex o f CcpA, which is a member of the GalR-Lacl family of bacterial regulat ory proteins, and the seryl-phosphorylated form of HPr (P-ser-HPr), as verified by recent studies on catabolite repression of the gnt operon . Analysis of the gnt promoter region by deletions and point mutations revealed that in addition to the cre in the first gene (gntR) of the gnt operon (cre(down)), this operon contains another cre located in th e promoter region (cre(up)). A translational gntR'-'lacZ fusion expres sed under the control of various combinations of wild-type and mutant cre(down) and cre(up) was integrated into the chromosomal amyE locus, and then catabolite repression of beta-galactosidase synthesis in the resultant integrants was examined. The in vivo results implied that ca tabolite repression exerted by cre(up) was probably independent of cat abolite repression exerted by cre(down); both cre(up) and cre(down) ca tabolite repression involved CcpA. Catabolite repression exerted by cr e(up) was independent of P-ser-HPr, and catabolite repression exerted by cre(down), was partially independent of P-ser-HPr. DNase I footprin ting experiments indicated that a complex of CcpA and P-ser-HPr did no t recognize cre(up), in contrast to its specific recognition of cre(do wn). However, CcpA complexed with glucose-6phosphate specifically reco gnized cre(up) as well as cre(down), but the physiological significanc e of this complexing is unknown.