Number of putative intronization and de-intronization events in fission yeasts.

aUnable to distinguish between intronization and de-intronization because of a lack of outgroup evidence.
bFor intronization, “Supported by transcriptome data” means that the novel intron region is spliced in at least one transcript. “Disproved by transcriptome data” means that the novel intron region is retained in all the related transcripts. For de-intronization, “Supported by transcriptome data” means the novel exon region is retained in at least one transcript. “Disproved by transcriptome data” means the novel exon region is spliced in all transcripts and is thus an unannotated intron. If no transcripts cover the novel intron or exon region, it is defined as “Lacking related transcript data”.