J. Bacteriol., 02 1996, 735-744, Vol 178, No. 3
Copyright © 1996, American Society for Microbiology

Repression of the Escherichia coli modABCD (molybdate transport) operon by ModE

AM Grunden, RM Ray, JK Rosentel, FG Healy and KT Shanmugam
Department of Microbiology and Cell Science, University of Florida, Gainesville 32611, USA.

The modABC gene products constitute the molybdate-specific transport system in Escherichia coli. Another operon coding for two proteins which diverges from the modABCD operon has been identified. The first gene of this operon codes for a 262-amino-acid protein, designated ModE (28 kDa), and the second genes codes for a 490-amino-acid protein. ModF (54 kDa). The role of ModF has not yet been determined; however, mutations in modE depressed modABCD transcription even in the presence of molybdate, suggesting that ModE is a repressor. ModE, in the presence of 1 mM molybdate, repressed the production of plasmid-encoded ModA and ModB' proteins in an in vitro transcription-translation system. DNA mobility shift experiments confirmed that ModE binds to an oligonucleotide derived from the operator region of the modABCD operon. Further experimentation indicated that ModE binding to target DNA minimally requires an 8-bp inverted-repeat sequence, TAAC GITA. A highly conserved amino acid sequence, TSARNOXXG (amino acids 125 to 133), was identified in ModE and homologs from Azotobacter vinelandii, Haemophilus influenzae, Rhodobacter capsulatus, and Clostridium pasterianum. Mutants with mutations in either T or G of this amino acid sequence were isolated as "superrepressor" mutants. These mutant proteins repressed modABCD transcription even in the absence of molybdate, which implies that this stretch of amino acids is essential for the binding of molybdate by the ModE protein. These results show that molybdate transport in E. coli is regulated by ModE, which acts as a repressor when bound to molybdate.

This article has been cited by other articles:

• Tejada-Jimenez, M., Llamas, A., Sanz-Luque, E., Galvan, A., Fernandez, E. (2007). A high-affinity molybdate transporter in eukaryotes. Proc. Natl. Acad. Sci. USA 104: 20126-20130 [Abstract] [Full Text]  
• Wiethaus, J., Wirsing, A., Narberhaus, F., Masepohl, B. (2006). Overlapping and Specialized Functions of the Molybdenum-Dependent Regulators MopA and MopB in Rhodobacter capsulatus. J. Bacteriol. 188: 8441-8451 [Abstract] [Full Text]  
• Delgado, M. J., Tresierra-Ayala, A., Talbi, C., Bedmar, E. J. (2006). Functional characterization of the Bradyrhizobium japonicum modA and modB genes involved in molybdenum transport. Microbiology 152: 199-207 [Abstract] [Full Text]  
• KAISER, B. N., GRIDLEY, K. L., NGAIRE BRADY, J., PHILLIPS, T., TYERMAN, S. D. (2005). The Role of Molybdenum in Agricultural Plant Production. ANN BOT (LOND) 96: 745-754 [Abstract] [Full Text]  
• Self, W. T., Hasona, A., Shanmugam, K. T. (2004). Expression and Regulation of a Silent Operon, hyf, Coding for Hydrogenase 4 Isoenzyme in Escherichia coli. J. Bacteriol. 186: 580-587 [Abstract] [Full Text]  
• Stewart, V., Bledsoe, P. J., Williams, S. B. (2003). Dual Overlapping Promoters Control napF (Periplasmic Nitrate Reductase) Operon Expression in Escherichia coli K-12. J. Bacteriol. 185: 5862-5870 [Abstract] [Full Text]  
• McNicholas, P. M., Gunsalus, R. P. (2002). The Molybdate-Responsive Escherichia coli ModE Transcriptional Regulator Coordinates Periplasmic Nitrate Reductase (napFDAGHBC) Operon Expression with Nitrate and Molybdate Availability. J. Bacteriol. 184: 3253-3259 [Abstract] [Full Text]  
• Self, W. T., Hasona, A., Shanmugam, K. T. (2001). N-terminal truncations in the FhlA protein result in formate- and MoeA-independent expression of the hyc (formate hydrogenlyase) operon of Escherichia coli. Microbiology 147: 3093-3104 [Abstract] [Full Text]  
• Anderson, L. A., McNairn, E., Leubke, T., Pau, R. N., Boxer, D. H. (2000). ModE-Dependent Molybdate Regulation of the Molybdenum Cofactor Operon moa in Escherichia coli. J. Bacteriol. 182: 7035-7043 [Abstract] [Full Text]  
• Lee, S., Reth, A., Meletzus, D., Sevilla, M., Kennedy, C. (2000). Characterization of a Major Cluster of nif, fix, and Associated Genes in a Sugarcane Endophyte, Acetobacter diazotrophicus. J. Bacteriol. 182: 7088-7091 [Abstract] [Full Text]  
• Cornish, A. S., Page, W. J. (2000). Role of Molybdate and Other Transition Metals in the Accumulation of Protochelin by Azotobacter vinelandii. Appl. Environ. Microbiol. 66: 1580-1586 [Abstract] [Full Text]  
• Phillips, N. J., Miller, T. J., Engstrom, J. J., Melaugh, W., McLaughlin, R., Apicella, M. A., Gibson, B. W. (2000). Characterization of Chimeric Lipopolysaccharides from Escherichia coli Strain JM109 Transformed with Lipooligosaccharide Synthesis Genes (lsg) from Haemophilus influenzae. J. Biol. Chem. 275: 4747-4758 [Abstract] [Full Text]  
• Grunden, A. M., Self, W. T., Villain, M., Blalock, J. E., Shanmugam, K. T. (1999). An Analysis of the Binding of Repressor Protein ModE to modABCD (Molybdate Transport) Operator/Promoter DNA of Escherichia coli. J. Biol. Chem. 274: 24308-24315 [Abstract] [Full Text]  
• Berlyn, M. K. B. (1998). Linkage Map of Escherichia coli K-12, Edition 10: The Traditional Map. Microbiol. Mol. Biol. Rev. 62: 814-984 [Abstract] [Full Text]  
• McNicholas, P. M., Mazzotta, M. M., Rech, S. A., Gunsalus, R. P. (1998). Functional Dissection of the Molybdate-Responsive Transcription Regulator, ModE, from Escherichia coli. J. Bacteriol. 180: 4638-4643 [Abstract] [Full Text]