STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF THE HUMAN FMR1 PROMOTERREVEALS SIMILARITIES WITH THE HNRNP-A2 PROMOTER REGION

Fragile X mental retardation syndrome is associated with an expansion of a CGG repeat within the 5'UTR of the first exon of the FMR1 gene, a bnormal methylation of the CpG island in the promoter region, and a tr anscriptional silencing of this gene, We studied transcriptional regul ation of the FMR1 gene using protein footprint analysis of the active and inactive gene in vivo, We identified four footprints within the FM R1 promoter region which correspond to consensus binding sites of know n transcription factors, alpha-PAL/NRF1, Sp1, H4TF1/Sp1-like and c-myc , These footprints were present in normal cells with a transcriptional ly active FMR1 gene, The same footprints were present in different cel l types: primary fibroblasts, lymphoblastoid cells and peripheral lymp hocytes, However, for the 1.1 kb region analyzed, no footprints were d etected in a variety of cell types derived from patients with fragile X syndrome which have a transcriptionally inactive FMR1 gene, A BLAST nucleotide search identified sequence similarities between the region of the FMR1 gene containing the footprints and an analogous region wit hin the promoter region of the gene for the heterogeneous nuclear ribo nucleoprotein (hnRNP) A2, a member of a family of ribonucleoproteins i mplicated in mRNA processing and nuclear-cytoplasm transport. The nucl eotide sequences identified in the hnRNP-A2 promoter region correspond to the same consensus binding sites showing DNA-protein interactions in the FMR1 gene, Our previous functional studies and the studies of o thers demonstrate that FMR proteins, like hnRNP-A2, are also ribonucle oproteins which appear to be involved in mRNA transport, The results f rom our footprint studies suggest that the expression of the FMR1 gene is regulated by the binding of specific transcription factors to sequ ence elements in the 5' region of the gene and that this expression ma y be regulated by elements in common with the hnRNP-A2 gene. Common re gulation of these two genes might play an important role in the cooper ative processing and transport of mRNA from the nucleus to the transla tion machinery.