title: The fragile X mental retardation protein is associated with poly(A)+ mRNA in actively translating polyribosomes.
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.
authors.affiliation: Pavillon Saint-Francois d'Assise du CHUQ, Département de biologie médicale, Faculté de médecine, Université Laval, Québec, Canada.
authors.forename: F
authors.initials: F
authors.lastname: Corbin
authors.forename: M
authors.initials: M
authors.lastname: Bouillon
authors.forename: A
authors.initials: A
authors.lastname: Fortin
authors.forename: S
authors.initials: S
authors.lastname: Morin
authors.forename: F
authors.initials: F
authors.lastname: Rousseau
authors.forename: E W
authors.initials: EW
authors.lastname: Khandjian
mesh_terms: D016475:3T3 Cells / Q000378:metabolism; D000818:Animals; D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D008607:Intellectual Disability / Q000235:genetics; D051379:Mice; D008856:Microscopy, Fluorescence; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D011061:Poly A / Q000235:genetics* / Q000378:metabolism; D011132:Polyribosomes / Q000235:genetics* / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D011061:Poly A; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C497683:FMR1 protein, human; C096915:FXR2 protein, human; C497684:Fmr1 protein, mouse