STRUCTURAL CHARACTERIZATION AND CHROMOSOMAL LOCATION OF THE GENE ENCODING HUMAN PLATELET GLYCOPROTEIN IB-BETA

Human platelet glycoprotein Ib beta (GPIb beta) (M(r) 22,000) is part of the GPIb-V-IX system that constitutes the receptor for von Willebra nd factor and mediates platelet adhesion in the arterial circulation. The four members of the receptor (GPs Ib alpha, Ib beta, V, and IX) sh are structural and functional features. Individually, GPIb beta contri butes to surface expression of the receptor and participates in transm embrane signaling through phosphorylation of its intracellular domain. To define the structure of the GPIb beta gene, a cosmid clone from a human genomic library was analyzed. The transcriptional start site was located by both primer extension and the ''anchored'' polymerase chai n reaction. Similar to the genes for Ib alpha, V, and IX, the Ib beta gene is compact with a single 274-base intron inserted into the 5' end of the open reading frame. The 5'-flanking region of the gene contain s both GATA and ets sites that are also found in the 5' promoter regio ns of other described megakaryocyte/platelet genes. The GPIb beta gene was localized to chromosome 22q11.2 by fluorescence in situ hybridiza tion. The GPIb beta gene has a simple structure, similar to that of ot her described megakaryocyte/platelet genes, including those of the GPI b-V-IX system.