Putative group I introns in the eukaryote nuclear internal transcribed spacers

Area of Science:

• Molecular Biology
• Genetics
• Evolutionary Biology

Background:

• Group I introns are mobile genetic elements known to interrupt genes in prokaryotes and eukaryotes.
• Introns have been identified in the small subunit (SSU) and large subunit (LSU) of rRNA operons but not previously in the Internal Transcribed Spacer (ITS) region.
• Unusually long ITS regions in certain fungi and unicellular organisms prompted further investigation.

Purpose of the Study:

• To investigate the cause of unusually long ITS regions in specific fungi and related unicellular organisms.
• To determine if Group I introns are present in the ITS regions of these organisms.
• To analyze the phylogenetic implications of intron presence in ITS regions.

Main Methods:

• Analysis of unusually long ITS sequences from fungi (Polychytrium aggregatum, Mitosporidium daphniae, Amoeboaphelidium occidentale, Nuclearia simplex) and shark species.
• Secondary structure prediction of identified insertions based on Group I intron models.
• Phylogenetic analysis incorporating conserved core structures and spacer introns.

Main Results:

• The increased length of the analyzed ITS sequences is attributed to the presence of introns within ITS-1 or ITS-2.
• Identified insertions exhibit secondary structures consistent with Group I introns.
• Phylogenetic analysis revealed that these introns cluster within conserved core structures.
• Removal of spacer introns allowed for the deduction of conventional ITS-2 structures in Mitosporidium, Amoeboaphelidium, and Nuclearia.
• Analysis of shark ITS sequences corroborated the findings, indicating congruent results.

Conclusions:

• Spacer regions, specifically ITS-1 and ITS-2, can harbor Group I introns.
• This discovery expands the known locations and potential mobility of Group I introns.
• The presence of introns in ITS regions has implications for phylogenetic analyses and understanding genome evolution.