Figure 4

Testing putative cases of group I intron reverse splicing. Phylogeny of fungal introns and analysis of rDNA flanking exons to assess putative cases of group I intron reverse splicing. A) Distance matrix phylogenetic tree of a reduced data set of 51 fungal introns. The results of a distance bootstrap analysis are shown above the branches on the left of the slash marks, whereas the results of a maximum likelihood bootstrap analysis are shown on the right of the slash marks. The values shown below the branches result from an unweighted maximum parsimony bootstrap analysis. The thick branches represent ≥95% Bayesian posterior probability. Branch lengths are proportional to the number of substitutions per site (see legend). The S. buchneri group I introns are marked with filled triangles and the P. perisidiosa introns are marked with the filled circles. The putative cases of intron movement are denoted with the filled squares on the internal nodes. The rDNA intron insertion site is shown for each ribozyme. B) Majority-rule consensus tree inferred from a Bayesian analysis of 34 fungal group I introns. Only the core regions of the ribozymes were used in this analysis. The colors for the different introns in panels A and B reflect the taxonomic position of the host cell containing the ribozymes (consistent with the scheme shown in Fig 2). C) Alignment of exon sequences (all from S. buchneri) at heterologous group I intron sites. Regions required for the IGS interaction that are implicated in reverse splicing intron movement are shown in the boxed areas.