Characterization of the 5′ end of the gene for human glucose phosphate isomerase (GPI)

We have isolated the gene coding for human glucose phosphate isomerase, and here we report the characterization of its 5′ end including the first two exons. The gene is greater than 50 kb in size and contains a minimum of eight exons. We have no evidence that this gene is part of a multigene family or that there are any pseudogenes. The potential transcription start site has been determined by primer extension analysis and is 52 bp upstream from the translation initiation site of the protein. Sequences 5′ to the transcription initiation site and within the first intron are extremely GC rich and form part of a CpG island. Five potential Sp1 sites (GGGCGG) have been located at positions −57, −61, −95, +183, and +575. The most 5′ of these (GGGGCGGGGG) is likely to be the main Sp1 binding site, as it conforms precisely to a 10-bp consensus sequence. At position −44 there is a putative TATA box (CATAAA). Thus in common with an increasing number of genes, the putative promoter region of glucose phosphate isomerase shows structural similarities to both housekeeping and facultative gene promoters.