STRUCTURE OF THE HUMAN GENE FOR THE NEURAL PHOSPHOPROTEIN-B-50 (GAP-43)

The genomic DNA encoding the exons for the human neural phosphoprotein B-50 (GAP-43) was isolated using rat-based cDNA probes and oligonucle otides. Exons 2 and 3 were isolated from a genomic library, exon 1 was amplified by PCR on total genomic DNA. The gene consists of 3 exons a nd 2 large introns. The first exon encodes the N-terminal 10 amino aci ds of B-50 involved in membrane association of the protein. Exon 2 enc odes the main part of the protein with the sites for protein kinase C- mediated phosphorylation and calmodulin binding, and includes a 10 ami no acid residue insert not found in rodents. Exon 3 encodes the last 2 9 amino acid residues. The reported sequence extends the known cDNA st ructure to both the 5' and 3' ends. The 358 bp region upstream of the translational initiation codon, containing the main transcription star ts, is purine-rich and does not include TATA or GC boxes. At the 3' en d potential polyadenylation signals were found 510 bp and 584 bp downs tream of the stopcodon in exon 3. The 5' end of the mRNA is heterogene ous in length, with primer extension products corresponding to a 5' un translated region of 159 and 343 bases. Northern hybridizations, howev er, indicate that the majority of B-50 mRNA has a shorter 5' untransla ted region, as was reported for the rat (Schrama et al., Soc. Neurosci . Abstr., 18 (1992) 333.4). The structural organization of the human g ene is similar to that described for the rat (Grabczyk et al., Eur. J. Neurosci. 2 (1990) 822-827), and both translated and untranslated reg ions show a high degree of sequence homology to the rat gene.