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J. Bacteriol. doi:10.1128/JB.00876-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The Expression and Association of Group IV Nitrogenase NifD and NifH Homologs in the Non-Nitrogen Fixing Archaeon Methanocaldococcus jannaschii

Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604; Departments of Biology and Chemistry, Washington University, Saint Louis, Missouri 63130; Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550; Virginia Bioinformatics Institute; and Departments of Biochemistry; and Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

^* To whom correspondence should be addressed. Email: Blankenship{at}wustl.edu.

	Abstract

Using genomic analysis, genes have been identified coding for proteins homologous to the structural proteins of nitrogenase (Raymond, J., Siefert, J. L., Staples, C. R. and Blankenship, R. E. 2004. Mol. Biol. Evol., 21: 541-554). The expression and association of NifD and NifH nitrogenase homologs (named NflD and NflH for ‘Nif-like’ D and H) has been detected in a non-nitrogen fixing hyperthermophilic methanogen, Methanocaldococcus jannaschii. These homologs are constitutively expressed and appear not to be directly involved with nitrogen metabolism or detoxification of compounds such as cyanide or azide. The NflH and NflD proteins were found to interact with each other, as determined by bacterial-two hybrid studies. Upon immunoisolation, NflD and NflH copurified along with three other proteins, whose functions are as yet uncharacterized. The apparent presence of genes coding for NflH and NflD in all known methanogens, their constitutive expression and their high sequence similarity to the NifH and NifD proteins or the BchL and BchN/B proteins suggest that NflH and NflD participate in (an) indispensable and fundamental function(s) in methanogens.