CHARACTERIZATION OF AN LRP-LIKE (LRPC) GENE FROM BACILLUS-SUBTILIS

In the course of the Bacillus subtilis genome sequencing project, we i dentified an open reading frame encoding a putative 16.4 kDa protein. This protein shows, respectively, 34% and 25% identity with the Escher ichia coli regulatory proteins Lrp and AsnC. Phylogenetic analysis sug gests that it represents a new group in the AsnC-Lrp family. Sequence comparisons, as well as immunodetection experiments, lead to the concl usion that the product of this B. subtilis lrp-like-gene is a bona fid e Lrp protein - the first one to be detected in gram-positive bacteria . When expressed in E. coli, the B. subtilis Lrp-like protein is able to repress, by about two-fold, the expression of the ilvIH operon whic h is normally regulated by E. coli Lrp, indicating functional similari ty in their regulatory targets. Vegetative growth of a B. subtilis lrp -like mutant is not affected in rich medium. However, the lrp-like mut ation causes a transitory inhibition of growth in minimal medium in th e presence of valine and isoleucine, which is relieved by leucine. Thi s points to a possible role in regulation of amino acid metabolism. In addition, sporogenesis occurs earlier in the lrp-like mutant than in the reference strain, implying that the B. subtilis Lrp-like protein p lays a role in the growth phase transition.