Nuclear Fragile X Mental Retardation Protein Interacting Protein 1 (NUFIP1)

Silenced expression of the FMR1 gene is responsible for fragile X syndrome. The FMR1 gene encodes an RNA-binding protein (FMRP) that can shuttle between the nucleus and the cytoplasm and is found associated with polysomes in the cytoplasm. NUFIP mRNA expression was found to be strikingly similar to that of the FMR1 gene in neurons of cortex, hippocampus, and cerebellum. At the subcellular level, NUFIP colocalized with nuclear isoforms of FMRP in a dot-like pattern. NUFIP contains a C2H2 zinc finger motif and a nuclear localization signal. In vitro, NUFIP showed RNA-binding activity. NUFIP did not interact with the FMRP homologs encoded by the FXR1 and FXR2 genes. These results indicated a specific nuclear role for FMRP.