Positions of introns along the protein sequence (panel A) and in the structure of the Cytochrome C Oxidase Subunit I (panel B). Panel A shows the conservation profile of the cytochrome C oxidase subunit I (see figure 1 for details). Blue dots indicate group I intron positions and orange dots represent group II intron positions. Panel B displays the structure of the Paracoccus denitrificans cytochrome C oxidase subunit I (PDB ID: 1QLE) colored according to site conservation. The arrow points to the intron insertion site of the intron found in the homologous protein in some vascular plants, protist, fungi, green algae, liverworts, and amoeba. The insertion site is between Gly275 and His276 (space-filled model). Panel C shows the relationship between the number of group I introns found at each position and the site conservation. Panel D shows the relationship between the number of group II introns found at each position and the site conservation.