Lineage-specific features of hemiascomycetous introns
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- Intron size is variable
Mean intron size varies widely within each yeast genome (depending on the intron population) [Spingola et al., 1999; Bon et al., 2003], but also varies according to the phylogenetic position of the yeast species: from 300 nt in the 'Saccharomyces-kluyveromyces' related species down to 90 nt in the most distant species, except in Y. lipolytica [Bon et al., 2003].
- An internal distance as evolutionary marker
The S2 internal distance, from the branch site to the 3' splice site, is proportional to the phylogenetic position of the yeast species : from 40 in S. cerevisiae down to 2 nt in Y. lipolytica, and could potentially serve as marker for gene evolution [Bon et al., 2003].
- Intron vocabulary is species-dependent
Although they originate from the same common ancestor, and share some common rules, each hemiascomycetous yeast species have subsequently developed its own intron signature in the course of evolution (i.e. the speciation) resulting in a species-dependent intron vocabulary [Bon et al., 2003] probably to optimise splicing efficiency and possibly gene expression.
- Yarrowia lipolytica introns are apart
They exhibit a large size, similar to that encounter in the 'Saccharomyces' related species, whereas small introns are thought to occur in this distant yeast species. Introns have a particular signature compared to their hemiascomycetes counterparts consisting in a distinct 5' splice site motif and a distinct nucleotide context around the splice sites [Bon et al., 2003].
- Ancestral nuclear genes in yeasts were mosaic genes.
The analysis of the degree of conservation of intron positions between homologous yeast genes clearly shows that ancestral nuclear yeast genes were probably multi-intronic, and that most introns have been lost during speciation in the hemiascomycetes since they separated from the last common ancestor with S. pombe [Bon et al., 2003].
It is probable that S. pombe have the archetype of the yeast nuclear gene exon/intron organisation [Kaufer & Potashkin, 2000], and that this architecture has diverged in the hemiascomycetes during speciation [Bon et al., 2003].
- The exon/intron architecture is evolutionary flexible.
The comparison of the evolutionary conservation of intron position in homologous yeast genes revealed that:
Last modified: Tue Feb 10 11:13:58 CET 2004