H-090. Global Effects of the Bacillus subtilis Fur-Regulated Small RNA, FsrA

G. T. Smaldone, J. D. Helmann;
Cornell Univ., Ithaca, NY.

In Bacillus subtilis, the ferric uptake regulator (Fur) is the major sensor of iron levels. One of the genes repressed by Fur encodes a small non-coding RNA (sRNA) named FsrA (Fur-regulated small RNA). FsrA and the putative Fur-regulated chaperones, FrcAB and FrcC (formerly YdbN and MrgC, respectively), are believed to regulate non-essential iron-containing enzymes thus prioritizing iron usage within the cell. Sequence comparisons demonstrate that several FsrA targets contain regions of complementarily consistent with regulation by direct FsrA-mRNA pairing. Transcriptome studies were employed to identify genes under the regulatory control of FsrA. Comparisons between the following mutant strains ((a) fur v. fur fsrA, (b) fur v. fur frcAB, (c) fur v. fur frcC, and (d) fur v. fur frcABC) were used to identify those genes whose repression is dependent on the FsrA small RNA (comparison a) and the role of the RNA chaperones in these effects (comparisons b - d). Functions regulated by FsrA include succinate dehydrogenase (sdhCBA), cytochrome bd biosynthesis (cydABCD), menaquinol:cytochrome c biosynthesis (qcrABC), and the suspected iron-sulfur containing proteins YvfVW-YvbY. Additionally, we have been able to determine subsets of the FsrA regulon dependent on either FrcAB or FrcC. To investigate the mechanism of activity of these putative chaperones we have overexpressed FrcAB and monitored its effects on FsrA-mRNA duplex formation. Initial results have lead to the hypothesis that an FrcA and FrcB form a heteromultimeric complex. Taken together, these results define the FsrA regulon in conjunction with its proposed chaperones and begin to elucidate the nature of the RNA-chaperone interaction.