Exon structure analysis.

Exon structure of the four already known sialidase subgroups (NEU1–4; grey bars), of the newly identified NEU5 sialidases (green bars), of the 5 sialidases from M. brevicollis (light blue bars) and of the NEU1 sialidases from hemichordate S. kowalevskii (yellow bars). Horizontal bars represent the protein sequence and the position of the exon junctions within the polypeptides are indicated by the black lines. Dotted black lines in NEU3 subgroup indicate additional exons found only in the avian species analyzed (G. gallus, T. guttata), while in NEU4 indicate an additional exon find only in X. tropicalis. The bar representation of the protein sequences is not in scale with the exon length, but the reciprocal position of exon junctions in different subgroups are respected.