In order to elucidate the function of the nifU gene product in nitrogenase
maturation in Azotobacter vinelandii. the gene product has been hyperexpressed in
Escherichia coli and characterized by various biophysical techniques. Following the
initial characterization, site-directed mutagenesis of conserved cysteinyl residues was
performed in order to gain further insight into the structure/function relationship of
NifU.
Both the Fe protein and the MoFe protein of nitrogenase require processing
by additional nif genes including nifM (Fe protein), and nifE, N, B, H, V, and Q
(MoFe protein). Two additional genes, nifU and nifS, are required for the
maturation of both nitrogenase component proteins. It has been proposed that they
may somehow be involved in metallocluster biosynthesis (Jacobson et al., 1989b).
Our laboratory has determined that the nifS gene product (Nifs) is a pyridoxal-phosphate
containing enzyme capable of catalyzing the desulfurization of L-cysteine
and can provide the inorganic sulfide necessary for in vitro metallocluster biosynthesis
of the Fe protein (Zheng, et al., 1993: Zheng, et al., 1994).
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