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Lsm proteins bind and stabilize RNAs containing 5' poly(A) tracts
Naomi Bergman1, Karen C M Moraes, John R Anderson
1Department of Microbiology, Immunology & Pathology, Colorado State University, Fort Collins, Colorado 80525, USA.
Nature Structural & Molecular Biology
|August 19, 2007
Summary
Orthopoxvirus messenger RNAs feature a unique 5' poly(A) tract that stabilizes them by blocking RNA decay pathways. The Lsm complex binds this tract, preventing degradation and influencing mRNA stability.
Area of Science:
- Molecular Biology
- Virology
- RNA Metabolism
Background:
- Many orthopoxvirus messenger RNAs (mRNAs) possess a non-templated polyadenosine (poly(A)) tract at their 5' end, a feature whose function remains unclear.
- This unusual 5' poly(A) tract ranges from 5 to 40 nucleotides in length.
- Understanding the role of this structural anomaly is crucial for comprehending viral RNA stability and cellular mRNA decay mechanisms.
Purpose of the Study:
- To investigate the functional significance of the 5' poly(A) tract in orthopoxvirus mRNAs.
- To elucidate the molecular mechanisms by which this feature affects RNA stability.
- To identify potential protein interactions involved in the stabilization process.
Main Methods:
- UV cross-linking assays to detect protein-RNA interactions.
- Biochemical binding assays using recombinant Lsm1-7 complex.
- RNA stability assays following Lsm1 knockdown in cellular models.
- Analysis of RNA decay pathways, including 3'-to-5' exonuclease activity and decapping.
Main Results:
- The 5' poly(A) tracts were found to repress RNA decay by inhibiting both 3'-to-5' exonucleases and RNA decapping.
- UV cross-linking confirmed the association of the Lsm complex with the 5' poly(A) tract.
- Recombinant Lsm1-7 complex specifically binds 5' poly(A) tracts of 10-21 nucleotides, correlating with the length required for stabilization.
- Lsm1 knockdown abolished the RNA stabilizing effect of the 5' poly(A) tract.
Conclusions:
- The Lsm complex binds to the 5' poly(A) tract of orthopoxvirus mRNAs, acting as a protective cap.
- This interaction prevents 3'-to-5' decay and decapping, thereby stabilizing the viral RNA.
- The findings suggest a novel mechanism where the Lsm complex bridges both ends of the mRNA, offering protection against degradation and have implications for cellular mRNA decay research.
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