The genomic organization of platelet glycoprotein IIIa.
The platelet membrane glycoprotein (GP) IIb/IIIa complex, a member of the integrin family of adhesive receptors involved in cell-cell and cell-matrix interactions, contains binding sites for fibrinogen, von Willebrand factor, fibronectin, and vitronectin. Absence or defects of this receptor result in the platelet bleeding disorder Glanzmann's thrombasthenia. In this report, we describe the isolation of genomic DNA coding for the entire mature GPIIIa protein. Mature GPIIIa is encoded by 14 exons which range in length from 90 to 3618 base pairs, which are contained within an approximately 46-kilobase (kb) stretch of genomic DNA on chromosome 17. All of the exon/intron junctions were found to conform to the consensus splice donor and acceptor sequences. The coding region of the GPIIIa gene is identical with the previously described cDNA sequence except for three silent substitutions. One substitution creates a TaqI site which may be the site of a known GPIIIa polymorphism. A second substitution eliminates a SmaI site. Aside from the start of the first exon described, which begins at the second base of the first codon of the mature protein, there is no correlation between the organization of the exons in this gene and proposed functional domains of the protein based on analysis of the primary amino acid sequence. The less frequently used polyadenylation signal AAATTAAA was present at the 3'-end of the major RNA transcript. Recently, an alternatively processed GPIIIa transcript has been described. We demonstrate that this transcript results from nonsplicing of the final intron. The description of the GPIIIa gene organization should be of importance in understanding the evolution of the integrin family of receptors and should be useful in the molecular biology analysis of thrombasthenic patients who have a defect in the GPIIIa gene.