The mechanism of introner-like element multiplication in fungi

The recent discovery of introner-like elements (ILEs) in six fungal species shed new light on the origin of regular spliceosomal introns (RSIs). ILEs are novel spliceosomal introns that are found in hundreds of near-identical copies in unrelated genes. They account for the vast majority of intron gains in these species and are not associated with intron losses. Remarkably, ILEs are longer than RSIs and harbor predicted stable secondary structures. However, they are prone to quickly degenerate in sequence and length to become undistinguishable from RSIs, suggesting that ILEs are predecessors of most RSIs. Further analyses are being performed in order to understand the multiplication mechanism of ILEs, which is hypothesized to resemble the retro-homing mechanism of self-splicing group II introns. The dynamics of ILE’s secondary structures could be predicted and two conserved motifs were identified in almost all fungal ILEs, which might play an important role in direct insertion into DNA. We also have developed a genetic screen in yeast in order to capture and characterize ILE insertion events. These ongoing studies should provide hints about the mechanism of ILE multiplication, i.e. how new spliceosomal introns are gained in fungi.