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Messenger RNA deadenylylation precedes decapping in mammalian cells
P Couttet1, M Fromont-Racine, D Steel
1Institut Jacques Monod du Centre National de la Recherche Scientifique, Université Paris 7, Tour 43, 2 Place Jussieu, 75251 Paris Cedex 05, France.
Abstract:
In yeast, the major mRNA degradation pathway is initiated by poly(A) tail shortening that triggers mRNA decapping. The mRNA is then degraded by 5'-to-3' exonucleolysis. In mammalian cells, even though poly(A) tail shortening also precedes mRNA degradation, the degradation pathway has not been elucidated. We have used a reverse transcription-PCR approach that relies on mRNA circularization to measure the poly(A) tail length of four mammalian mRNAs. This approach allows for the simultaneous analysis of the 5' and 3' ends of the same mRNA molecule. For all four mRNAs analyzed, this strategy permitted us to demonstrate the existence of small amounts of decapped mRNA species which have a shorter poly(A) tail than their capped counterparts. Kinetic analysis of one of these mRNAs indicates that the decapped species with a short poly(A) tail are mRNA degradation products. Therefore, our results indicate that decapping is preceded by a shortening of the poly(A) tail in mammalian cells, as it is in yeast, suggesting that this mRNA degradation pathway is conserved throughout eukaryotic evolution.
Insights
Mammalian mRNA degradation involves poly(A) tail shortening, triggering decapping. This study confirms this conserved pathway, revealing decapped mRNA species with shorter poly(A) tails.
Area of Science:
- Molecular Biology
- Eukaryotic Gene Expression
Background:
- mRNA degradation is crucial for gene regulation.
- In yeast, degradation begins with poly(A) tail shortening and decapping.
- The mammalian mRNA degradation pathway remains largely unelucidated.
Purpose of the Study:
- To investigate the mRNA degradation pathway in mammalian cells.
- To determine if poly(A) tail shortening precedes decapping in mammals.
- To assess the conservation of mRNA degradation mechanisms across eukaryotes.
Main Methods:
- Developed a novel reverse transcription-PCR (RT-PCR) approach.
- Utilized mRNA circularization to analyze mRNA ends simultaneously.
- Measured poly(A) tail length in four different mammalian mRNAs.
Main Results:
- Identified small amounts of decapped mRNA species in mammalian cells.
- Demonstrated that decapped mRNAs possess shorter poly(A) tails than capped mRNAs.
- Kinetic analysis confirmed decapped, short-tailed mRNAs are degradation intermediates.
Conclusions:
- Poly(A) tail shortening precedes mRNA decapping in mammalian cells.
- This pathway appears conserved between yeast and mammalian mRNA degradation.
- Suggests a conserved eukaryotic mechanism for mRNA turnover.