Fig. 3

Mitochondrial ND5 gene organization and ND5-717 intron secondary structure in Ricordea yuma and Amplexidiscus fenestrafer. a Secondary structure diagrams of ND5-717 group I introns in R. yuma (left) and A. fenestrafer (right). The ten conserved paired segments of the catalytic core (P1 to P10) are shown and flanking ND5 exons sequences are in red letters. The P8 extensions containing mitochondrial genes are indicated. The blue circles indicate catalytic core sequences at the G-binding site and in small red circles are nucleotides substitutions in A. fenestrafer compared to R. yuma. b Organization map of mitochondrial ND5 gene in Corallimorpharian. A schematic view of the ND5-717 ribozyme is presented above the map. The splice sites are distant apart, but brought in proximity in a permuted intron–exon order due to the circular organization of the mtDNAs. Thus, ND5 exon 2 is presented upstream of ND5 exon 1. ND5 mRNA consisting of the ligated exons with the splicing junction indicated is shown below. Chromatograms of the exon ligation sequences are shown for R. yuma (left) and A. fenestrafer (right)