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Group II Introns Generate Functional Chimeric Relaxase Enzymes with Modified Specificities through Exon Shuffling at
Félix LaRoche-Johnston1, Rafia Bosan1, Benoit Cousineau1
1Department of Microbiology and Immunology, McGill University, Montréal, Québec, Canada.
Molecular Biology and Evolution
|October 29, 2020
Summary
Group II introns generate novel functional proteins by shuffling genetic material through RNA trans-splicing. This process enhances bacterial conjugation efficiency, demonstrating a gain-of-function for hosts.
Area of Science:
- Molecular Biology
- Genetics
- RNA Biology
Background:
- Group II introns are large, self-splicing RNA enzymes.
- They are ancient mobile elements and proposed ancestors of significant portions of the human genome.
- Bacterial group II introns were previously viewed as selfish genetic parasites.
Purpose of the Study:
- To investigate the functional consequences of group II intron-mediated intergenic trans-splicing in bacteria.
- To determine if chimeric proteins generated by this pathway exhibit altered functions.
- To explore the role of group II introns in generating bacterial genetic diversity.
Main Methods:
- Studied Ll.LtrB and Ef.PcfG group II introns from Lactococcus lactis and Enterococcus faecalis.
- Analyzed intergenic trans-splicing to form chimeric relaxase mRNAs and proteins.
- Assessed the efficiency of resulting chimeric relaxase enzymes in bacterial conjugation.
- Examined chimeric gene structures and expression levels under natural conditions.
Main Results:
- Ll.LtrB and Ef.PcfG introns catalyze the formation of chimeric relaxase mRNAs and functional proteins via intergenic trans-splicing.
- Some chimeric relaxase enzymes exhibited gain-of-function phenotypes, significantly enhancing bacterial conjugation.
- Shuffled functional domain relaxase enzymes were produced under natural expression levels.
- Identified lactococcal chimeric relaxase genes with precise intron insertion site junctions.
Conclusions:
- Group II introns generate genetic diversity through RNA trans-splicing and DNA recombination.
- This process can create novel functional enzymes with shuffled exons, leading to gain-of-function phenotypes.
- Group II introns actively contribute to bacterial evolution and adaptation by generating functional novelty.
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