Fig. 4.

FsrA sRNA and Fbp proteins mediate iron sparing response in B. subtilis. The FsrA RNA is expressed under iron-poor conditions, when iron-dependent Fur repression is relieved. FsrA in turn represses several target genes, including the six examples shown in this figure. Fur also represses expression of three small basic proteins, FbpAB and FbpC; the fsrA, fbpAB, and fbpC transcripts are unlinked on the chromosome. The Fbp proteins make variable contributions to FsrA regulation, as indicated by the − and + signs. For one fbpAB-dependent target, lutABC, FbpB specifically has been shown to be required for FsrA-mediated regulation.