The fragile X mental retardation protein binds specifically to its mRNA via a purine quartet motif

Fragile X syndrome is caused by the absence of protein FMRP, the function of which is still poorly understood. Previous studies have suggested that FMRP may be involved in various aspects of mRNA metabolism, including transport, stability, and/or translatability. FMRP was shown to interact with a subset of brain mRNAs as well as with its own mRNA; however, no specific RNA-binding site could be identified precisely. Here, we report the identification and characterization of a specific and high affinity binding site for FMRP in the RGG-coding region of its own mRNA. This site contains a purine quartet motif that is essential for FMRP binding and can be substituted by a heterologous quartet-forming motif. The specific binding of FMRP to its target site was confirmed further in a reticulocyte lysate through its ability to repress translation of a reporter gene harboring the RNA target site in the 5'-untranslated region. Our data address interesting questions concerning the role of FMRP in the post-transcriptional control of its own gene and possibly other target genes.