On the function of the CGG-binding protein

From the nuclei of human HeLa cells, we have isolated a 20 kDa protein which binds specifically to 5′-d(CGG)n-3′ repeats, either in synthetic oligodeoxyribonucleotides or in the 5′-untranslated region of the FMR1 (fragile X mental retardation 1) gene on human chromosome Xq27.3. The loss of the FMR1 gene product has been implicated in the causation of the fragile X syndrome in humans. In electrophoretic mobility shift assays, the sequence specificity and methylation sensitivity of the 5′-d(CGG)n-3′-binding protein (CGGBP1) were documented. When the CGGBP1 was overexpressed in HeLa cells, the FMR1-promoter in constructs carrying this promoter and the endogenous FMR1 promoter were inhibited. The inhibition depended on the length of a 5′-d(CGG)n-3′ repeat in the FMR1-promoter constructs. A fusion protein consisting of the green fluorescent protein (GFP) and the CGGBP1 associated preferentially with the telomers of the short arms of the acrocentric human chromosomes 13, 14, 15, 21 and 22. Their telomers carry the genes for the 28S rRNA which contain 5′-d(CGG)n-3′ repeats. We currently search for additional targets for CGGBP1 binding in the human genome by using the DNA microarray technique. The amino acid sequence of three peptides in the CGGBP1 gene was determined and an available EST clone was used for cloning the human and murine CGGBP1 genes. Protein database searches did not reveal any related sequences. The nucleotide sequence of the translated region of the CGGBP1 gene from healthy, premutation and full mutation carrying fragile X individuals was determined, but mutations were not detected.