Fig. 3. Alignments of hb zinc fingers and putative NREs from different species. Alignment of orthologous zinc fingers from different species reveals that the various fingers are highly related across species in the position of structural residues. Alignments are shown of (A) the two NF fingers, (B) the four MF fingers and (C) the two CF metal-binding fingers. Black arrowheads indicate the structural residues of the putative metal binding fingers. The spacing between cysteine and histidine residues within and between each finger in each cluster (N, M and C) is shown at the top of each section of the figure. (D) Alignment of ExF, an additional putative zinc-finger identified in the C. elegans and H. triserialis Hb sequences. These fingers are in analogous positions in their respective proteins, but have little structural similarity to each other. (E) DNA nucleotide alignment of predicted nanos response element (NRE) sequences from the 3'UTR of hb transcripts of various species. D.v. and D.m. 1 and 2 indicate the two NRE sequences found in the 3'UTR of both of these Drosophila species. (F) Overall structure of Hb, with regard to zinc fingers. The putative H. triserialis Hb-coding sequence was reconstructed from the published genomic sequence (Savage and Shankland, 1996) by comparison with the grasshopper and C. elegans hb sequences, and manual assignment of splice junctions. This process yields a predicted leech Hb of similar structure to C. elegans Hb. As the overall structure illustrated for L. migratoria and S. americana is conserved across phyla, it may be the ancestral insect structure, with the NF fingers being lost in the lineage leading to Tribolium and Drosophila. Whether or not the ExF fingers are part of an ancestral protostome structure is less clear, as the leech and C. elegans ExF fingers lack noticeable similarity. Species used are L.m., L. migratoria; S.a., S. americana; C.e., C. elegans; H.t., H. triserialis (leech); D.m., D. melanogaster; T.c., T. castaneum (flour beetle); M.d., M. domestica (house fly); and D.v., D. virilis.
