Recurrent insertion of 5′-terminal nucleotides and loss of the branchpoint motif in lineages of group II introns inserted in mitochondrial preribosomal RNAs

Secondary structure models of (A) the G. frondosa SSU788 intron, (B) the P. fulgens SSU788 intron. (Boldface) Nucleotides in common between the two introns. (Arrowheads) Point to splice junctions; (asterisk) points to the branchpoint of the Grifola intron. Labeling of secondary structure components and tertiary interactions is as in Michel et al. (2009). In domain IV, nucleotides not shown were replaced by the sequence CTCGAG in “ORF-less” constructs.