First unraveling of the hidden and intricate evolutionary history of a bacterial group II intron family.

Bacterial group II introns are large RNA enzymes that self-splice from primary transcripts. Following excision, they can invade various DNA target sites using RNA-based mobility pathways. As fast evolving retromobile elements, which move between genetic loci within and across species, their evolutionary history was proved difficult to study and infer.

Molecular characterization of both transesterification reactions of the group II intron circularization pathway.

Group II introns can self-splice from RNA transcripts through branching, hydrolysis and circularization, being released as lariats, linear introns and circles, respectively. In contrast to branching, the circularization pathway is mostly based on assumptions and has been largely overlooked. Here, we address the molecular details of both transesterification reactions of the group II intron circularization pathway in vivo.

Group II Introns Generate Functional Chimeric Relaxase Enzymes with Modified Specificities through Exon Shuffling at Both the RNA and DNA Level.

Group II introns are large self-splicing RNA enzymes with a broad but somewhat irregular phylogenetic distribution. These ancient retromobile elements are the proposed ancestors of approximately half the human genome, including the abundant spliceosomal introns and non-long terminal repeat retrotransposons. In contrast to their eukaryotic derivatives, bacterial group II introns have largely been considered as harmful selfish mobile retroelements that parasitize the genome of their host.

Conjugation as a Highly Sensitive Assay to Study Group II Intron Splicing In Vivo.

Group II introns are noncoding sequences that interrupt genes, and that must be removed or spliced-out at the RNA level during gene expression. Following the transcription of interrupted genes, group II introns self-splice while concurrently ligating their flanking exons to generate mature mRNAs ready for translation. Ll.

Detection of Group II Intron-Generated Chimeric mRNAs in Bacterial Cells.

Chimeric RNAs are the transcripts composed of exons from two separate genes or transcripts. Although the presence of these joined RNA molecules have mainly been documented in a variety of eukaryotes, we recently demonstrated that the Ll.LtrB group II intron, from the gram-positive bacterium Lactococcus lactis, can generate chimeric mRNAs through a novel intergenic trans-splicing pathway.

Bacterial group II introns generate genetic diversity by circularization and trans-splicing from a population of intron-invaded mRNAs.

Group II introns are ancient retroelements that significantly shaped the origin and evolution of contemporary eukaryotic genomes. These self-splicing ribozymes share a common ancestor with the telomerase enzyme, the spliceosome machinery as well as the highly abundant spliceosomal introns and non-LTR retroelements. More than half of the human genome thus consists of various elements that evolved from ancient group II introns, which altogether significantly contribute to key functions and genetic diversity in eukaryotes.

Recent horizontal transfer, functional adaptation and dissemination of a bacterial group II intron.

Background: Group II introns are catalytically active RNA and mobile retroelements present in certain eukaryotic organelles, bacteria and archaea. These ribozymes self-splice from the pre-mRNA of interrupted genes and reinsert within target DNA sequences by retrohoming and retrotransposition. Evolutionary hypotheses place these retromobile elements at the origin of over half the human genome.

The Ll.LtrB intron from Lactococcus lactis excises as circles in vivo: insights into the group II intron circularization pathway.

Group II introns are large ribozymes that require the assistance of intron-encoded or free-standing maturases to splice from their pre-mRNAs in vivo. They mainly splice through the classical branching pathway, being released as RNA lariats. However, group II introns can also splice through secondary pathways like hydrolysis and circularization leading to the release of linear and circular introns, respectively.