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The fragile X mental retardation protein is associated with poly(A)+ mRNA in actively translating polyribosomes
F Corbin1, M Bouillon, A Fortin
1Pavillon Saint-Francois d'Assise du CHUQ, Département de biologie médicale, Faculté de médecine, Université Laval, Québec, Canada.
Abstract:
The fragile X syndrome results from a transcriptional silencing of the FMR1 gene and the absence of its encoded protein. FMRP is a cytoplasmic RNA-binding protein, whose specific cellular function is still unknown. We present evidence that virtually all detectable cytoplasmic FMRP in mouse NIH 3T3 and human HeLa cells is found strictly in association with mRNA in actively translating polyribosomes. Furthermore, FMRP released from polyribosomes is associated with ribonucleoprotein complexes with sedimentation coefficients of 60-70S and selection on oligo(dT)-cellulose reveals that this association is specific to poly(A)-containing mRNPs. This association with actively translating polyribosomes is not affected by alteration of translational processes induced by serum stimulation and starvation in NIH 3T3 cells, suggesting that FMR1 expression is not cell cycle regulated and that FMRP might have a house-keeping function. FXR2 protein, which is closely related to FMRP, is also detected associated with mRNPs in translating polyribosomes. The results strongly suggest that FMRP might be a mRNA chaperone interacting with mRNP complexes.
Insights
Fragile X syndrome is linked to the FMR1 gene. Research shows the Fragile X mental retardation protein (FMRP) binds to messenger RNA (mRNA) in translating polyribosomes, suggesting a role as an mRNA chaperone.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Fragile X syndrome stems from FMR1 gene silencing and FMRP absence.
- The precise cellular function of FMRP, a cytoplasmic RNA-binding protein, remains undetermined.
Purpose of the Study:
- To investigate the cellular localization and function of FMRP.
- To explore the association of FMRP with mRNA and its potential role in translation.
Main Methods:
- Cellular fractionation to isolate polyribosomes.
- Biochemical analysis of ribonucleoprotein complexes.
- Oligo(dT)-cellulose chromatography to assess mRNA binding specificity.
Main Results:
- Cytoplasmic FMRP is predominantly found associated with mRNA in actively translating polyribosomes in NIH 3T3 and HeLa cells.
- FMRP forms 60-70S ribonucleoprotein complexes with poly(A)-containing messenger ribonucleoprotein particles (mRNPs).
- FMRP association with polyribosomes is independent of cell cycle regulation, indicating a potential house-keeping function.
Conclusions:
- FMRP likely functions as an mRNA chaperone, interacting with mRNP complexes during active translation.
- The findings provide insights into the molecular mechanisms underlying Fragile X syndrome.
- FXR2 protein, similar to FMRP, also associates with mRNPs in translating polyribosomes.