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.

The circle to lariat ratio of the Ll.LtrB group II intron from Lactococcus lactis is greatly influenced by a variety of biological determinants in vivo.

Bacterial group II introns mostly behave as versatile retromobile genetic elements going through distinct cycles of gain and loss. These large RNA molecules are also ribozymes splicing autocatalytically from their interrupted pre-mRNA transcripts by two different concurrent pathways, branching and circularization. These two splicing pathways were shown to release in bacterial cells significant amounts of branched intron lariats and perfect end-to-end intron circles respectively.

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.

Circularization pathway of a bacterial group II intron.

Group II introns are large RNA enzymes that can excise as lariats, circles or in a linear form through branching, circularization or hydrolysis, respectively. Branching is by far the main and most studied splicing pathway while circularization was mostly overlooked. We previously showed that removal of the branch point A residue from Ll.

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.

Isolation and characterization of functional tripartite group II introns using a Tn5-based genetic screen.

Background: Group II introns are RNA enzymes that splice themselves from pre-mRNA transcripts. Most bacterial group II introns harbour an open reading frame (ORF), coding for a protein with reverse transcriptase, maturase and occasionally DNA binding and endonuclease activities. Some ORF-containing group II introns were shown to be mobile retroelements that invade new DNA target sites.

Impact of diet and stress on the development of preeclampsia-like symptoms in p57kip2 mice.

The cyclin-dependent kinase inhibitor p57(kip2) regulates the cell cycle of trophoblastic cells. It has been established by a Japanese group that the heterozygous p57(kip2) knockout (p57(-/+)) mice are a good model of preeclampsia as they develop hypertension, proteinuria, and placental pathology. However, apart from the placental pathology, we could not observe these symptoms in our laboratory.