Numbers refer to the conserved cysteines in the Azotobacter vinelandii IscU sequence. Fully conserved residues are shaded in black. The LPPVK sequences that are required for IscU interactions with HscA and the histidine (NifU and IscU) and lysine (SufU) residues in the cluster binding pocket are shaded in grey. Av,Azotobacter vinelandii; Ec, Escherichia coli; Hi, Haemophilus influenzae; At, Arabidopsis thaliana; Sc, Saccharomyces cerevisiae; Hs, Homo sapiens; Sp, Streptococcus pyogenes; Bs, Bacillus subtilis; Tm, Thermotoga maritima.