Multifunctional polyribosome-associated RNA-binding protein that plays a central role in neuronal development and synaptic plasticity through the regulation of alternative mRNA splicing, mRNA stability, mRNA dendritic transport and postsynaptic local protein synthesis of a subset of mRNAs (PubMed:11438589, PubMed:12032354, PubMed:15475576, PubMed:16631377, PubMed:16790844, PubMed:17417632, PubMed:17548835, PubMed:18539120, PubMed:18653529, PubMed:19640847, PubMed:19166269, PubMed:20159450, PubMed:21784246, PubMed:23235829, PubMed:24813610). Plays a role in the alternative splicing of its own mRNA (PubMed:18653529). Plays a role in mRNA nuclear export (PubMed:16790844). Together with export factor NXF2, is involved in the regulation of the NXF1 mRNA stability in neurons (PubMed:17548835). Stabilizes the scaffolding postsynaptic density protein DLG4/PSD-95 and the myelin basic protein MBP mRNAs in hippocampal neurons and glial cells, respectively; this stabilization is further increased in response to metabotropic glutamate receptor (mGluR) stimulation (PubMed:17417632). Plays a role in selective delivery of a subset of dendritic mRNAs to synaptic sites in response to mGluR activation in a kinesin-dependent manner (PubMed:18539120). Plays a role as a repressor of mRNA translation during the transport of dendritic mRNAs to postsynaptic dendritic spines (PubMed:11376146, PubMed:12581522, PubMed:14570712, PubMed:12927206, PubMed:15475576, PubMed:16908410, PubMed:18805096, PubMed:19640847, PubMed:21784246, PubMed:23235829). Component of the CYFIP1-EIF4E-FMR1 complex which blocks cap-dependent mRNA translation initiation (PubMed:18805096). Represses mRNA translation by stalling ribosomal translocation during elongation (PubMed:21784246). Reports are contradictory with regards to its ability to mediate translation inhibition of (MBP) mRNA in oligodendrocytes (PubMed:14613971, PubMed:23891804). Also involved in the recruitment of the RNA helicase MOV10 to a subset of mRNAs and hence regulates microRNA (miRNA)-mediated translational repression by AGO2 (PubMed:20159450, PubMed:25464849). Facilitates the assembly of miRNAs on specific target mRNAs (By similarity). Also plays a role as an activator of mRNA translation of a subset of dendritic mRNAs at synapses (PubMed:14614133, PubMed:14613971, PubMed:15548614, PubMed:19640847, PubMed:19166269, PubMed:21490210). In response to mGluR stimulation, FMR1-target mRNAs are rapidly derepressed, allowing for local translation at synapses (PubMed:16908410, PubMed:17507556, PubMed:19640847). Binds to a large subset of dendritic mRNAs that encode a myriad of proteins involved in pre- and postsynaptic functions (PubMed:11719188, PubMed:11376146, PubMed:14613971, PubMed:17507556, PubMed:21784246, PubMed:21490210, PubMed:24349419). Binds to 5'-ACU[GU]-3' and/or 5'-[AU]GGA-3' RNA consensus sequences within mRNA targets, mainly at coding sequence (CDS) and 3'-untranslated region (UTR) and less frequently at 5'-UTR (By similarity). Binds to intramolecular G-quadruplex structures in the 5'- or 3'-UTRs of mRNA targets (PubMed:25692235). Binds to G-quadruplex structures in the 3'-UTR of its own mRNA (By similarity). Binds also to RNA ligands harboring a kissing complex (kc) structure; this binding may mediate the association of FMR1 with polyribosomes (By similarity). Binds mRNAs containing U-rich target sequences (By similarity). Binds to a triple stem-loop RNA structure, called Sod1 stem loop interacting with FMRP (SoSLIP), in the 5'-UTR region of superoxide dismutase SOD1 mRNA (PubMed:19166269). Binds to the dendritic, small non-coding brain cytoplasmic RNA 1 (BC1); which may increase the association of the CYFIP1-EIF4E-FMR1 complex to FMR1 target mRNAs at synapses (PubMed:12581522, PubMed:18805096). Associates with export factor NXF1 mRNA-containing ribonucleoprotein particles (mRNPs) in a NXF2-dependent manner (PubMed:17548835). Binds to a subset of miRNAs in the brain (PubMed:20159450). May associate with nascent transcripts in a nuclear protein NXF1-dependent manner (By similarity). In vitro, binds to RNA homomer; preferentially on poly(G) and to a lesser extent on poly(U), but not on poly(A) or poly(C) (By similarity). Moreover, plays a role in the modulation of the sodium-activated potassium channel KCNT1 gating activity (PubMed:20512134). Negatively regulates the voltage-dependent calcium channel current density in soma and presynaptic terminals of dorsal root ganglion (DRG) neurons, and hence regulates synaptic vesicle exocytosis (By similarity). Modulates the voltage-dependent calcium channel CACNA1B expression at the plasma membrane by targeting the channels for proteosomal degradation (PubMed:24709664). Plays a role in regulation of MAP1B-dependent microtubule dynamics during neuronal development (PubMed:15475576). Recently, has been shown to play a translation-independent role in the modulation of presynaptic action potential (AP) duration and neurotransmitter release via large-conductance calcium-activated potassium (BK) channels in hippocampal and cortical excitatory neurons (PubMed:25561520). Finally, FMR1 may be involved in the control of DNA damage response (DDR) mechanisms through the regulation of ATR-dependent signaling pathways such as histone H2AX/H2A.x and BRCA1 phosphorylations (PubMed:24813610). Homodimer (By similarity). Forms heterodimer with FXR1; heterodimerization occurs in a methylation-dependent manner (By similarity). Forms heterodimer with FXR2 (By similarity). Homooligomer (By similarity). Component of the CYFIP1-EIF4E-FMR1 complex at least composed of CYFIP, EIF4E and FMR1; this mRNA cap binding complex formation increases in presence of the brain cytoplasmic RNA BC1 and is dynamically regulated in an activity-dependent manner to repress and then possibly release dendritic mRNAs for translation in response to mGluR stimulation (PubMed:18805096). Associates with the SMN core complex that contains SMN, GEMIN2/SIP1, DDX20/GEMIN3, GEMIN4, GEMIN5, GEMIN6, GEMIN7, GEMIN8 and STRAP/UNRIP (PubMed:18093976). Part of a ribonucleoprotein complex with AGO2/EIF2C2 and miRNAs (By similarity). Interacts with AGO2/EIF2C2 (By similarity). Interacts (via C-terminus) with CACNA1B; this interaction induces a decrease in the number of presynaptic functional CACNA1B channels at the cell surface (PubMed:24709664). Interacts with CYFIP1; this interaction recruits CYFIP1 to capped mRNA (PubMed:11438699, PubMed:18805096). Interacts with CYFIP2 (PubMed:11438699). Interacts with EIF5; this interaction occurs in a RNA-dependent manner (By similarity). Interacts with dynein (PubMed:18539120). Interacts with FXR1 and FXR2 (PubMed:10567518). Interacts with methylated histone H3 (By similarity). Interacts with IGF2BP1; this interaction allows to recruit IGF2BP1 to mRNA in a FMR1-dependent manner (By similarity). Interacts (via N-terminus) with KCNMB4 (PubMed:25561520). Interacts with KCNT1 (via C-terminus); this interaction alters gating properties of KCNT1 (PubMed:20512134). Interacts (via C-terminus) with KIF5A; this interaction is increased in a mGluR-dependent manner (PubMed:18539120). Interacts (via phosphorylated form) with MCRS1 (via N-terminus) (By similarity). Interacts with MOV10; this interaction is direct, occurs in an RNA-dependent manner on polysomes and induces association of MOV10 with RNAs (PubMed:25464849). Interacts with MYO5A and PURA; these interactions occur in association with polyribosome (PubMed:12147688). Interacts with NCL (PubMed:10567518). Interacts with NUFIP1 (PubMed:10556305). Interacts (via N-terminus) with NUFIP2 (By similarity). Interacts with NXF1; this interaction occurs in a mRNA-dependent and polyribosome-independent manner in the nucleus (By similarity). Interacts with NXF2 (via N-terminus); this interaction is direct and occurs in a NXF1 mRNA-containing mRNP complexes (PubMed:16790844, PubMed:17548835). Interacts with RANBP9; this interaction is direct and inhibits binding of FMR1 to RNA homomer (PubMed:15381419). Interacts with RPLP0 (PubMed:21784246). Interacts (via C-terminus) with SMN (via C-terminus); this interaction is direct and occurs in a RNA-independent manner (By similarity). Interacts with TDRD3 (via C-terminus); this interaction is direct (By similarity). Interacts with YBX1; this interaction occurs in association with polyribosome (PubMed:11162447). Interacts with nucleosome (By similarity). Associates with polyribosome; this association occurs in a mRNA-dependent manner (PubMed:8842725, PubMed:9285783, PubMed:12581522, PubMed:12575950, PubMed:14613971, PubMed:15317853, PubMed:15805463, PubMed:21784246). Associates with messenger ribonucleoprotein particles (mRNPs) (PubMed:8842725, PubMed:9285783, PubMed:11719188, PubMed:12581522, PubMed:12575950, PubMed:15329415, PubMed:18805096). Associates with microtubules in a kinesin- and dynein-dependent manner (PubMed:18539120). Interacts with HABP4 (By similarity). Colocalizes with H2AX/H2A.x in pericentromeric heterochromatin in response to DNA damaging agents (PubMed:24813610). Localizes on meiotic pachytene-stage chromosomes (PubMed:24813610). Forms nuclear foci representing sites of ongoing DNA replication in response to DNA damaging agents (PubMed:24813610). Shuttles between nucleus and cytoplasm in a XPO1/CRM1-dependent manner (PubMed:8895584, PubMed:8842725). Localizes to cytoplasmic granules, also referred to as messenger ribonucleoprotein particles or mRNPs, along dendrites and dendritic spines (PubMed:15028757, PubMed:16631377). FMR1-containing cytoplasmic granules colocalize to F-actin-rich structures, including filopodium, spines and growth cone during the development of hippocampal neurons (By similarity). FMR1-containing cytoplasmic granules are transported out of the soma along axon and dendrite to synaptic contacts in a microtubule- and kinesin-dependent manner (PubMed:15312650, PubMed:16098134, PubMed:18539120). Colocalizes with CACNA1B in the cytoplasm and at the cell membrane of neurons (PubMed:24709664). Colocalizes with CYFIP1, CYFIP2, NXF2 and ribosomes in the perinuclear region (PubMed:11438699, PubMed:16790844). Colocalizes with CYFIP1 and EIF4E in dendrites and probably at synapses (PubMed:18805096). Colocalizes with FXR1, kinesin, 60S acidic ribosomal protein RPLP0 and SMN in cytoplasmic granules in the soma and neurite cell processes (By similarity). Colocalizes with FXR1 and FXR2 in discrete granules, called fragile X granules (FXGs), along axon and presynaptic compartments (PubMed:19193898). Colocalizes with TDRD3 in cytoplasmic stress granules (SGs) in response to various cellular stress (By similarity). Interacts with SND1 (By similarity). Expressed in brain (PubMed:8033209). Strongly expressed in the neonatal hippocampus (PubMed:15475576). Expressed in the brainstem (PubMed:14613971). Expressed in the cerebellum (PubMed:19193898). Expressed in neurons of hippocampal area CA3 (PubMed:17548835, PubMed:19193898). Expressed in neurons of the olfactory bulb including the granule, mitral, tufted and juxtaglomerular cells (PubMed:19193898). Expressed in both mature and immature olfactory sensory neurons (OSNs) (PubMed:19193898). Expressed in neurons in all layers and in all regions of cerebral cortex (PubMed:19193898). Expressed in mature oligodendrocytes (OLGs) (PubMed:23891804). Expressed in spermatogonia (at protein level) (PubMed:16790844). Expressed predominantly in the brain (PubMed:16000371). Expressed in testis (PubMed:8033209). Rapidly and transiently up-regulated in response to metabotropic glutamate receptor activation in a protein synthesis-dependent manner in neurons (at protein level). The N-terminal 134 amino acids are necessary for homodimerization and RNA-binding. The N-terminal 298 amino acids are sufficient to interact with KCNMB4 and to regulate presynaptic action potential (AP) duration in neurons. The two agenet-like domains are necessary for binding to histone H3 in a methylation-dependent manner. The KH domains are necessary for mediating miRNA annealing to specific RNA targets. The KH 2 domain is necessary for binding to kissing complex (kc) RNA ligands. The RGG box domain is necessary for binding to mRNA targets that contain G-quadruplex structures. The RGG-box domain is necessary for binding to a triple stem-loop RNA structure, called Sod1 stem loop interacting with FMRP (SoSLIP), in the superoxide dismutase SOD1 mRNA. The RGG box domain is necessary for binding to its own mRNA. The RGG-box domain is necessary for binding to homomer poly(G). Phosphorylated on several serine residues (PubMed:14570712). Phosphorylation at Ser-499 is required for phosphorylation of other nearby serine residues (PubMed:14570712). Phosphorylation has no effect on the binding of individual mRNA species, but may affect the association with polyribosome (PubMed:14570712). Unphosphorylated FMR1 is associated with actively translating polyribosome, whereas a fraction of phosphorylated FMR1 is associated with apparently stalled polyribosome (PubMed:14570712). Dephosphorylation by an activated phosphatase may release the FMR1-mediated translational repression and allow synthesis of a locally required protein at snypases (PubMed:14570712). Monoubiquitinated (PubMed:16908410). Polyubiquitinated (PubMed:16908410). Ubiquitinated and targeted for proteasomal degradation after activation of metabotropic glutamate receptor (mGluR) (PubMed:16908410). Monomethylated and asymmetrically dimethylated at four arginine residues of the arginine-glycine-glycine box. Methylation disrupts the binding of FMRP to RNAs through its RGG box (PubMed:16319129). Methylation is necessary for heterodimerization with FXR1, association with polyribosomes, recruitment into stress granules and translation of FMR1 target mRNAs. Methylated by PRMT1, PRMT3 and PRMT4, in vitro (PubMed:16319129). Show normal fertility (PubMed:8033209). Display enlarged testes and ovaries (PubMed:8033209, PubMed:23235829). Display learning deficits and hyperactivity, in the absence of gross pathological abnormalities of the brain (PubMed:8033209). Display immature neurons with excess of long, thin growth cone filopodia and dendritic filopodia and spine protrusions with less synaptic contacts (PubMed:9144249, PubMed:11438589, PubMed:16631377, PubMed:17417632, PubMed:18539120). Show no increase in the number of dendritic filopodia-spine protrusions in response to KCL-mediated depolarization (PubMed:16631377). Display alterations in the appearance, distribution and volume of nuclear speckles (PubMed:24349419). Display enhanced metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD) in the hippocampus (PubMed:11438589, PubMed:16908410, PubMed:12032354). Leads to excessive presynaptic action potential (AP) broadening in hippocampal and cortical neurons (PubMed:25561520). Show alteration in the splicing pattern of its own FMR1 mRNA in the cortex (PubMed:18653529). Alters the abundance and subcellular distribution of a subset of mRNAs in the brain (PubMed:12575950, PubMed:17417632). Display a reduction in the recruitment of certain FMR1 target mRNAs in actively translating polyribosomes at synapses (PubMed:12575950, PubMed:17507556). Display decreased delivery of specific mRNAs into dendrites in mGluR-stimulated neurons (PubMed:18539120). Display a delayed MAPB1 protein expression decline in the developing hippocampus (PubMed:15475576). Show a relief of ribosome stalling on dendritic FMR1 target mRNAs (PubMed:21784246). Display enhanced postsynaptic protein synthesis of a subset of FMR1 target mRNAs (PubMed:12581522, PubMed:16908410, PubMed:19640847, PubMed:21784246). Unable to induce postsynaptic protein synthesis of a subset of FMR1 mRNA targets in response to mGluR activation (PubMed:16908410, PubMed:17507556). Display enhanced presynaptic protein synthesis of the voltage-dependent calcium channel CACNA1B (PubMed:24709664). Display also enhanced protein synthesis of a subset of FMR1 target mRNAs in ovaries (PubMed:23235829). Display reduced postsynaptic protein synthesis of a subset of FMR1 target mRNAs (PubMed:12927206, PubMed:14614133, PubMed:19640847, PubMed:19166269, PubMed:21490210). Display reduced general protein synthesis in synapses in response to mGluR activation (PubMed:15548614). Show brain-region specific reduction in the expression and/or localization of FAM206A/Simiate (PubMed:24349419). Display similar myelin basic protein (MBP) nexpression level in brain cerebrum than in wild-type mice (PubMed:23891804). Display an absence of nuclear foci on meiotic pachytene-stage chromosomes (PubMed:24813610). Show incomplete resolution of single-strand repair intermediates, crossing over and pairing of homologous chromosomes during meiotic prophase in a subset of spermatocytes (PubMed:24813610). Belongs to the FMR1 family.