Fig 4.

A. Conserved nucleotides at 5' and 3' ends of introns of Tetrahymena, Ichthyophthirius, Paramecium, Oxytricha, and Stylonychia [5–10]. For each intron, a 5 bp long exon part was also considered. B. Strength of the 5' and 3' splice site motif as a function of the intron length. The strength of the splice site motif was calculated as the entropy of its frequency matrix, see the main text. Red and black boxplots designate the entropy measure of 5' and 3' splice sites, respectively. In order to account for uneven sample size, for each intron length up to 200 bp, we randomly sampled 50 introns 50 times and estimated their average splice sites entropy. Intron length intervals with less than 50 introns were excluded.