Genomic arrangement of the mouse GP Ibα gene. Restriction enzyme analysis of a P1 plasmid containing a fragment of mouse genomic DNA identified contiguous BamHI andBamHI/EcoRI restriction fragments that were chosen for DNA sequence determination. Based on sequence alignment with the human GP Ibα gene, boundaries for two exons are proposed (boxed regions) with an open reading frame (shaded box) encoding the putative mouse GP Ibα precursor polypeptide.19 A shaded gray region under the schematic representation of the gene identifies the approximate position of a radiolabeled fragment used for Northern analysis (Fig 2). The nucleotide sequence has been deposited in GenBank (accession no.U91967).