Bacterial group II introns: splicing, function and evolution

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The goal of our research program is to study splicing, function and evolutionary questions related to bacterial group II introns. In a first initiative we study trans-splicing of group II introns in order to address the evolutionary relationships between group II introns, nuclear introns and the five small RNAs that are part of the splicing machinery, the spliceosome. Secondly, we are exploring the various splicing pathways of group II introns in bacterial cells. Finally, we study the dissemination of these retromobile elements by conjugation and transduction between bacterial species. Our model system is the Ll.LtrB group II intron from Lactococcus lactis. L. lactis is an industrially important low G+C Gram-positive bacterium mainly used in the dairy industry for the production of cheese and yogurt. Ll.LtrB was found associated with different conjugative elements in L. lactis: the pRS01 and pAH90 plasmids and the chromosomal sex factor. We are thus studying if the transfer by conjugation of the L. lactis sex factor between bacterial cells can support the spread of the Ll.LtrB intron it conveys. We also study if the Ll.LtrB intron can be disseminated in the bacterial kingdom by various bacteriophages (transduction). After transfer of the intron-carrying elements from L. lactis to different bacterial species, we will study the reinsertion of the Ll.LtrB mobile group II intron in its new cell environment. Reinsertion of the Ll.LtrB intron into homologous and non-homologous sites will be studied. We are also studying the various splicing pathways of group II introns in bacterial cells and their capacity to be fragmented and still splice in trans. This will allow us to address the origin of nuclear introns and their splicing machinery. These studies will address the evolutionary theories claiming that group II introns are the ancestors of both the nuclear introns of eukaryotes and the five snRNAs that are part of the spliceosome and shed light on the importance of horizontal transfer in the evolution and phylogenetic distribution of group II introns.