Group I introns are widespread in archaea

Area of Science:

• Molecular Biology
• Genomics
• Evolutionary Biology

Background:

• Group I catalytic introns are prevalent in bacterial, viral, organellar, and eukaryotic genomes, but were previously thought to be absent in archaea.
• Archaea were known to possess bulge-helix-bulge (BHB) introns, with a few exceptions of group II introns.
• BHB introns are hypothesized to have evolved from extinct group I intron ancestors, similar to the proposed origin of eukaryotic spliceosomal introns from group II introns.

Purpose of the Study:

• To investigate the presence of group I introns in archaeal genomes.
• To challenge the long-held assumption of group I intron absence in archaea.
• To explore the evolutionary relationships between different intron types across life domains.

Main Methods:

• Utilized an advanced computational homology search method incorporating conserved sequence and RNA secondary structure.
• Applied this method to analyze a wide range of archaeal phyla.
• Focused on identifying introns that were difficult to detect using standard sequence similarity searches.

Main Results:

• Identified 39 group I introns across diverse archaeal phyla.
• Found instances where both group I introns and BHB introns coexist within the same host gene.
• Demonstrated the utility of structure-aware computational methods for discovering evolutionarily conserved but sequence-divergent genetic elements.

Conclusions:

• Group I introns are present in archaea, expanding their known phylogenetic distribution.
• The co-occurrence of group I and BHB introns in the same gene suggests potential complex evolutionary histories or functional interactions.
• This discovery necessitates a re-evaluation of intron evolution models and highlights the importance of advanced bioinformatics tools in uncovering hidden genomic diversity.