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Mechanisms of Intron Loss and Gain in the Fission Yeast Schizosaccharomyces

Authors
Journal
PLoS ONE
1932-6203
Publisher
Public Library of Science
Publication Date
Volume
8
Issue
4
Identifiers
DOI: 10.1371/journal.pone.0061683
Keywords
  • Research Article
  • Biology
  • Computational Biology
  • Genomics
  • Comparative Genomics
  • Genome Complexity
  • Genome Evolution
  • Evolutionary Biology
  • Genomic Evolution
  • Genetics
  • Gene Splicing
  • Model Organisms
  • Yeast And Fungal Models
  • Schizosaccharomyces Pombe
Disciplines
  • Biology

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.

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