RNA-binding protein required for embryonic and postnatal development of muscle tissue (PubMed:30770808). May regulate intracellular transport and local translation of certain mRNAs (By similarity). Interacts with FMR1 (PubMed:8668200, PubMed:7489725, PubMed:11157796). Interacts with FRX2 (PubMed:7489725). Interacts with TDRD3 (PubMed:18664458). Interacts with HABP4 (PubMed:21771594). Interacts with CYFIP2 but not with CYFIP1 (By similarity). (Microbial infection) Interacts with Sindbis virus non-structural protein 3 (via C-terminus); this interaction inhibits the formation of host stress granules on viral mRNAs and the nsp3-FXR1 complexes bind viral RNAs and probably orchestrate the assembly of viral replication complexes. Adjacent to Z-lines in muscles. Alternative splicing appears to be tissue-specific. Expressed in all tissues examined including heart, brain, kidney and testis. The tandem Agenet-like domains preferentially recognize trimethylated histone peptides. Arg-445 is dimethylated, probably to asymmetric dimethylarginine. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the FMR1 family.