Mutations in of have been shown to deregulate expression of several genes that are normally repressed by iron. A conserved sequence, the iron-responsive operator (IRO), was identified near promoters of (involved in the synthesis of the siderophore vicibactin), (specifies an ECF factor needed for vicibactin synthesis) and the two genes (encoding vicibactin receptor). Removal of these IRO sequences abolished Fe-responsive repression. Most of these genes were constitutively expressed in the heterologous host, , but introduction of the cloned gene repressed expression of these genes in this heterologous host if the corresponding IRO sequences were also intact. These observations are the first to examine the mechanisms of RirA, which has no sequence similarity to well-known iron-responsive regulators such as Fur or DtxR. They provide strong circumstantial evidence that RirA is a transcriptional regulator that binds to -acting regulatory sequences near the promoters of at least some of the genes whose expression it controls in response to Fe availability.


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  1. Allaway, D., Schofield, N. A., Leonard, M. E., Gilardoni, L., Finan, T. M. & Poole, P. S.(2001). Use of differential fluorescence induction and optical trapping to isolate environmentally induced genes. Environ Microbiol 3, 397–406.[CrossRef] [Google Scholar]
  2. Andrews, S. C., Robinson, A. K. & Rodriguez-Quinones, F.(2003). Bacterial iron homeostasis. FEMS Microbiol Rev 27, 215–237.[CrossRef] [Google Scholar]
  3. Beringer, J. E.(1974). R factor transfer in Rhizobium leguminosarum. J Gen Microbiol 84, 188–198.[CrossRef] [Google Scholar]
  4. Carter, R. A., Worsley, P. S., Sawers, G. & 7 other authors(2002). The vbs genes that direct synthesis of the siderophore vicibactin in Rhizobium leguminosarum: their expression in other genera requires ECF σ factor RpoI. Mol Microbiol 44, 1153–1166.[CrossRef] [Google Scholar]
  5. Chao, T.-C., Becker, A., Buhrmester, J., Pühler, A. & Weidner, S.(2004). The Sinorhizobium meliloti fur gene regulates with dependence of Mn(II) the transcription of the sitABCD operon encoding a metal type transporter. J Bacteriol 186, 3609–3620.[CrossRef] [Google Scholar]
  6. Diaz-Mireles, E., Wexler, M., Sawers, G., Bellini, D., Todd, J. D. & Johnston, A. W. B.(2004). The Fur-like protein Mur of Rhizobium leguminosarum is a Mn(2+)-responsive transcriptional regulator. Microbiology 150, 1447–1456.[CrossRef] [Google Scholar]
  7. Johnston, A. W. B., Yeoman, K. H. & Wexler, M.(2001). Metals and the rhizobial-legume symbiosis – uptake, utilization and signalling. Adv Microbial Physiol 45, 113–156. [Google Scholar]
  8. Keon, R. G., Fu, R. & Voordouw, G.(1997). Deletion of two downstream genes alters expression of the hmc operon of Desulfovibrio vulgaris subsp. vulgaris Hildenborough. Arch Microbiol 167, 376–383.[CrossRef] [Google Scholar]
  9. Kolade, O. O., Bellini, P., Wexler, M., Johnston, A. W. B., Grossmann, J. G. & Hemmings, A. M.(2002). Structural studies of the Fur protein from Rhizobium leguminosarum. Biochem Soc Trans 30, 771–774. [Google Scholar]
  10. Lawrence, J. G. & Hendrickson, H.(2003). Lateral gene transfer: when will adolescence end? Mol Microbiol 50, 739–749.[CrossRef] [Google Scholar]
  11. Lynch, D., O'Brien, J., Welch, T., Clarke, P., Cuiv, P. O., Crosa, J. H. & O'Connell, M.(2001). Genetic organization of the region encoding regulation, biosynthesis, and transport of rhizobactin 1021, a siderophore produced by Sinorhizobium meliloti. J Bacteriol 183, 2576–2585.[CrossRef] [Google Scholar]
  12. Masse, E. & Gottesman, S.(2002). A small RNA regulates the expression of genes involved in iron metabolism in Escherichia coli. Proc Natl Acad Sci U S A 99, 4620–4625.[CrossRef] [Google Scholar]
  13. McHugh, J. P., Rodriguez-Quinones, F., Abdul-Tehrani, H., Svistunenko, D. A., Poole, R. K., Cooper, C. E. & Andrews, S. C.(2003). Global iron-dependent gene regulation in Escherichia coli: a new mechanism for iron homeostasis. J Biol Chem 278, 29478–29486.[CrossRef] [Google Scholar]
  14. Messing, J., Crea, R. & Seeburg, P. H.(1983). A system for shotgun DNA sequencing. Nucleic Acids Res 9, 309–314. [Google Scholar]
  15. Outten, F. W., Djaman, O. & Storz, G.(2004). A suf operon requirement for Fe-S cluster assembly during iron starvation in Escherichia coli. Mol Microbiol 52, 861–872.[CrossRef] [Google Scholar]
  16. Pohl, E., Haller, J. C., Mijovilovich, A., Meyer-Klaucke, W., Garman, E. & Vasil, M. L.(2003). Architecture of a protein central to iron homeostasis: crystal structure and spectroscopic analysis of the ferric uptake regulator. Mol Microbiol 47, 903–915.[CrossRef] [Google Scholar]
  17. Sawers, G. & Böck, A.(1989). Novel transcriptional control of the pyruvate formate-lyase gene: upstream regulatory sequences and multiple promoters regulate anaerobic expression. J Bacteriol 171, 2485–2498. [Google Scholar]
  18. Schwartz, C. J., Giel, J. L., Patschkowski, T., Luther, C., Ruzicka, F. J., Beinert, H. & Kiley, P. J.(2001). IscR, an Fe-S cluster-containing transcription factor, represses expression of Escherichia coli genes encoding Fe-S cluster assembly proteins. Proc Natl Acad Sci U S A 18, 14895–14900. [Google Scholar]
  19. Spaink, H. P., Okker, R. J. H., Wijffelman, C. A., Pees, E. & Lugtenberg, B. J. J.(1987). Promoters in the nodulation region of the Rhizobium leguminosarum symbiotic plasmid pRL1JI. Plant Mol Biol 9, 27–39.[CrossRef] [Google Scholar]
  20. Stevens, J. B., Carter, R. A., Hussain, H., Carson, K. C., Dilworth, M. J. & Johnston, A. W. B.(1999). The fhu genes of Rhizobium leguminosarum, specifying siderophore uptake proteins: fhuDCB are adjacent to a pseudogene version of fhuA. Microbiology 145, 593–601.[CrossRef] [Google Scholar]
  21. Todd, J. D., Wexler, M., Sawers, G., Yeoman, K. H., Poole, P. S. & Johnston, A. W. B.(2002). RirA, an iron-responsive regulator in the symbiotic bacterium Rhizobium leguminosarum. Microbiology 148, 4059–4071. [Google Scholar]
  22. Toledano, M. B., Kullik, I., Tringh, F., Baird, P. T., Schneider, T. D. & Storz, G.(1994). Redox-dependent shift of OxyR-DNA contacts along an extended DNA-binding site: a mechanism for differential promoter selection. Cell 78, 897–909.[CrossRef] [Google Scholar]
  23. Wexler, M., Yeoman, K. H., Stevens, J. B., de Luca, N. G., Sawers, G. & Johnston, A. W. B.(2001). The Rhizobium leguminosarum tonB gene is required for the uptake of siderophore and haem as sources of iron. Mol Microbiol 41, 801–816. [Google Scholar]
  24. Wexler, M., Todd, J. D., Kolade, O., Bellini, D., Hemmings, A. M., Sawers, G. & Johnston, A. W. B.(2003). Fur is not the global regulator of iron uptake genes in Rhizobium leguminosarum. Microbiology 149, 1357–1365.[CrossRef] [Google Scholar]
  25. Yeoman, K. H., May, A. G., de Luca, N. G., Stuckey, D. B. & Johnston, A. W. B.(1999). A putative ECF sigma factor gene, rpoI, regulates siderophore production in Rhizobium leguminosarum. Mol Plant–Microbe Interact 12, 994–999.[CrossRef] [Google Scholar]
  26. Yeoman, K. H., Wisniewski-Dye, F., Timony, C., Stevens, J. B., deLuca, N. G., Downie, J. A. & Johnston, A. W. B.(2000). Analysis of the Rhizobium leguminosarum siderophore-uptake gene fhuA: differential expression in free-living bacteria and nitrogen-fixing bacteroids and distribution of an fhuA pseudogene in different strains. Microbiology 146, 829–837. [Google Scholar]
  27. Yeoman, K. H., Mitelheiser, S., Sawers, G. & Johnston, A. W. B.(2003). The ECF sigma factor RpoI of R. leguminosarum initiates transcription of the vbsGSO and vbsADL siderophore biosynthetic genes in vitro. FEMS Microbiol Lett 223, 239–244.[CrossRef] [Google Scholar]

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