Figure 1.

Schematic representation of NifU and different forms of NifU. The uppermost line represents full-length NifU. Above the line are indicated the cysteine (C) and aspartate (D) residues relevant to the present work. The numerical residue positions are indicated below the line. Substituting residues present in altered forms of NifU or NifU-1 are indicated by a bold, underlined letter at the appropriate position. Dashed brackets at the top of the figure indicate the respective mononuclear iron/transient [2Fe-2S] cluster domain and permanent [2Fe-2S] cluster domain within the NifU primary sequence.