Schematic representation of the coding exon structure of selected vertebrate Ngbs and several invertebrate globins.

<p>The coding exons and the corresponding protein alignments are printed in red and blue, respectively. Black lines indicate introns. Vertebrate Ngb genes consist of four highly conserved coding exons and three introns at positions B12.2, E11.0 and G7.0. The globins from <i>Ciona intestinalis</i> also possess a central intron at position E10.2. However, this intron is not orthologous to the central intron in Ngb genes. Abbreviations are explained in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047972#pone.0047972.s005" target="_blank">Table S1</a>.