title: Mechanisms of intron loss and gain in the fission yeast Schizosaccharomyces.
abstract: The fission yeast, Schizosaccharomyces pombe, is an important model species with a low intron density. Previous studies showed extensive intron losses during its evolution. To test the models of intron loss and gain in fission yeasts, we conducted a comparative genomic analysis in four Schizosaccharomyces species. Both intronization and de-intronization were observed, although both were at a low frequency. A de-intronization event was caused by a degenerative mutation in the branch site. Four cases of imprecise intron losses were identified, indicating that genomic deletion is not a negligible mechanism of intron loss. Most intron losses were precise deletions of introns, and were significantly biased to the 3' sides of genes. Adjacent introns tended to be lost simultaneously. These observations indicated that the main force shaping the exon-intron structures of fission yeasts was precise intron losses mediated by reverse transcriptase. We found two cases of intron gains caused by tandem genomic duplication, but failed to identify the mechanisms for the majority of the intron gain events observed. In addition, we found that intron-lost and intron-gained genes had certain similar features, such as similar Gene Ontology categories and expression levels.
authors.affiliation: MOE Key Laboratory for Biodiversity Science and Ecological Engineering and Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Zhu
authors.forename: Deng-Ke
authors.initials: DK
authors.lastname: Niu
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D017124:Conserved Sequence / Q000235:genetics; D020440:Gene Duplication / Q000235:genetics; D005800:Genes, Fungal / Q000235:genetics; D007438:Introns / Q000235:genetics*; D058977:Molecular Sequence Annotation; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010802:Phylogeny; D022821:RNA Splice Sites / Q000235:genetics; D048348:Reverse Transcription / Q000235:genetics; D012568:Schizosaccharomyces / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000235:genetics; D017384:Sequence Deletion / Q000235:genetics; D059467:Transcriptome / Q000235:genetics
chemical_list: D022821:RNA Splice Sites; D029702:Schizosaccharomyces pombe Proteins