Group I NifD sequences surrounding the His and Cys residues that attach the MoFe cofactor to the protein.

*GI is the NCBI Geninfo identifier.**The residue numbers shown, His-442 and Cys-275 refer to the sequence of Azotobacter vinelandii (GI: 758358) NifD. In the nitrogenase multiple sequence alignment (Figure S1) the corresponding residue numbers are His-562 and Cys-330. Invariant residues are shown in bold face.***Azospirillum brasilense NifD (GI:142417) sequence shows a Ser residue in the position of the invariant Cys residue. Examination of the entire sequence suggests that this may either be a sequence error or that the sequence is that of a mutant NifD.