Characterization of LrpC DNA-binding properties and regulation of Bacillussubtilis lrpC gene expression

The lrpC gene was identified during the Bacillus subtilis genome sequencing project. Previous experiments suggested that LrpC has a role in sporulatio n and in the regulation of amino acid metabolism and that it shares feature s with Escherichia coli Lrp, a transcription regulator (C. Beloin, S. Ayora , R. Exley, L. Hirschbein, N. Ogasawara, Y. Kasahara, J. C. Alonso, and F. Le Hegarat, Mol. Gen. Genet, 256:63-71, 1997). To characterize the interact ions of LrpC with DNA, the protein was overproduced and purified. We show t hat LrpC binds to multiple sites in the upstream region of its own gene wit h a stronger affinity for a region encompassing P1, one of the putative pro moters identified (P1 and P2). By analyzing lrpc-lacZ transcriptional fusio ns, we demonstrated that P1 is the major in vivo promoter and that, unlike many members of the lrp/asnC family, lrpC is not negatively autoregulated b ut rather slightly positively autoregulated. Production of LrpC in vivo is low in both rich and minimal media (50 to 300 LrpC molecules per cell). In rich medium, the cellular LrpC content is six- to sevenfold lower during th e exponentional phase than during the stationary growth phase. Possible det erminants and the biological significance of the regulation of lrpC express ion are discussed.