ASSOCIATION OF FMRP WITH RIBOSOMAL PRECURSOR PARTICLES IN THE NUCLEOLUS

The fragile X syndrome, one of the most common forms of inherited ment al retardation, is caused by an expansion of a polymorphic CGG repeat upstream the coding region of the FMR1 gene. These expansions are asso ciated with hypermethylation of the FMR1 gene, which results in the ab sence of the gene product, the FMR1 protein (FMRP). The physiological function of FMRP remains to be determined. We studied the ultrastructu ral localization of FMRP at the electron microscopical level using the immunogold technique. FMRP is associated with ribosomes attached to t he endoplasmic reticulum and with ribosomes free in the cytoplasm. In addition, MRP is found in the nucleus where the protein is associated with the granular component of the nucleolus. The cellular function of FMRP is hypothesized in relation to its subcellular distribution. (C) 1996 Academic Press, Inc.