This Article Full Text Full Text (PDF) Supplemental material Other Versions of this Article: JB.01734-06v1 189/7/2854    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dos Santos, P. C. Articles by Dean, D. R. Search for Related Content PubMed PubMed Citation Articles by Dos Santos, P. C. Articles by Dean, D. R.

 Previous Article  |  Next Article 

Journal of Bacteriology, April 2007, p. 2854-2862, Vol. 189, No. 7
0021-9193/07/$08.00+0     doi:10.1128/JB.01734-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Controlled Expression of nif and isc Iron-Sulfur Protein Maturation Components Reveals Target Specificity and Limited Functional Replacement between the Two Systems ^,

Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

Received 10 November 2006/ Accepted 16 January 2007

The nitrogen-fixing organism Azotobacter vinelandii contains at least two systems that catalyze formation of [Fe-S] clusters. One of these systems is encoded by nif genes, whose products supply [Fe-S] clusters required for maturation of nitrogenase. The other system is encoded by isc genes, whose products are required for maturation of [Fe-S] proteins that participate in general metabolic processes. The two systems are similar in that they include an enzyme for the mobilization of sulfur (NifS or IscS) and an assembly scaffold (NifU or IscU) upon which [Fe-S] clusters are formed. Normal cellular levels of the Nif system, which supplies [Fe-S] clusters for the maturation of nitrogenase, cannot also supply [Fe-S] clusters for the maturation of other cellular [Fe-S] proteins. Conversely, when produced at the normal physiological levels, the Isc system cannot supply [Fe-S] clusters for the maturation of nitrogenase. In the present work we found that such target specificity for IscU can be overcome by elevated production of NifU. We also found that NifU, when expressed at normal levels, is able to partially replace the function of IscU if cells are cultured under low-oxygen-availability conditions. In contrast to the situation with IscU, we could not establish conditions in which the function of IscS could be replaced by NifS. We also found that elevated expression of the Isc components, as a result of deletion of the regulatory iscR gene, improved the capacity for nitrogen-fixing growth of strains deficient in either NifU or NifS.

Published ahead of print on 19 January 2007.

Supplemental material for this article may be found at http://jb.asm.org/.

This article has been cited by other articles:

• Bandyopadhyay, S., Naik, S. G., O'Carroll, I. P., Huynh, B.-H., Dean, D. R., Johnson, M. K., Dos Santos, P. C. (2008). A Proposed Role for the Azotobacter vinelandii NfuA Protein as an Intermediate Iron-Sulfur Cluster Carrier. J. Biol. Chem. 283: 14092-14099 [Abstract] [Full Text]  
• Zhao, D., Curatti, L., Rubio, L. M. (2007). Evidence for nifU and nifS Participation in the Biosynthesis of the Iron-Molybdenum Cofactor of Nitrogenase. J. Biol. Chem. 282: 37016-37025 [Abstract] [Full Text]  
• Shimomura, Y., Kamikubo, H., Nishi, Y., Masako, T., Kataoka, M., Kobayashi, Y., Fukuyama, K., Takahashi, Y. (2007). Characterization and Crystallization of an IscU-type Scaffold Protein with Bound [2Fe 2S] Cluster from the Hyperthermophile, Aquifex aeolicus. J Biochem 142: 577-586 [Abstract] [Full Text]