Primary sequence features of the E. histolytica IscU and IscS proteins. A. Schematic drawing of the E. histolytica IscU and IscS protein sequences indicating the positions and sizes of Pfam  signature motifs PF01592 (NifU-N), PF04324 ([2Fe-2S]), and PF01106 (NifU-like) on the putative IscU protein and Pfam motif PF00266 (aminotransferase class V – AtV) on the putative IscS protein. The presence of these domains on a protein is used by the various databases to classify a protein and to infer its function. B. Comparison of the E. histolytica IscU protein depicted as above with homologous proteins from Azotobacter vinelandii (NifU), Campylobacter jejuni (NifU), Rickettsia prowazekii (NifU and RP667), Saccharomyces cerevisiae (Isu1 and Nfu1), and Homo sapiens (IscU2 and HIRIP5).