Publication: Fragile X related protein 1 isoforms differentially modulate the affinity of fragile X mental retardation proteins for G-quartet RNA structure.

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Fragile X syndrome, the most frequent form of inherited mental retardation, is due to the absence of expression of the Fragile FMRP is involved in several steps of mRNA metabolism: nucleocytoplasmic trafficking, translational control and transport along dendrites in neurons. Fragile Here we analyze the ability of three isoforms of FXR1P, expressed in different tissues, to bind G-quartet RNA structure specifically. Only the longest FXR1P isoform was found to be able to bind specifically the G-quartet RNA, albeit with a lower affinity as compared to FMRP, whereas the other two isoforms negatively regulate the affinity of FMRP for G-quartet RNA. This result is important to decipher the molecular basis of fragile X syndrome, through the understanding of FMRP action in the context of its multimolecular complex in different tissues. In addition, we show that the action of FXR1P is synergistic rather than compensatory for FMRP function.