Figure 3.

Asplenium nidus and Marsilea drummondii cDNA sequences identify the splice sites of the nad2 introns and show several RNA editing sites in the flanking exon sequences. Location of the group II intron is indicated by an arrowhead. Intron binding sites IBS1 and IBS2 are overlined. A total of 11 C-to-U RNA editing events (u) and one reverse exchange (c) modify the RNA sequence in Asplenium and reconstitute conserved amino acid codons. Nucleotide and amino acid differences in Marsilea are shown above the Asplenium sequence. The single editing event in Marsilea is not observed in Asplenium, but reconstitutes a cysteine codon conserved in Oenothera. The Marsilea and Asplenium nad2 sequences have been deposited in the database under accession nos. Y07910Y07910 and Y07911Y07911, respectively.