CHARACTERIZATION OF THE GENE FOR HUMAN HISTIDINE-RICH GLYCOPROTEIN

Abstract

Human histidine-rich glycoprotein (HRG) is a single-chain glycoprotein in plasma which is considered to modulate a coagulation and fibrinolysis system with the ability to bind to heparin, plasminogen, fibrinogen, thrombospondin, etc. Recently we have elucidated the primary structure of HRG by determining the nucleotide sequence of its cDNA, and showed that HRG is composed of several different types of internal repeats, each one of which shows considerable homology with the functional and/or structural domains of other proteins including high molecular weight kininogen, antithrombin III, cystatins, and proline-rich protein and peptide. Thus, the multifunctional property of HRG was suggested to be due to its multi-domain structure. In the present studies, a human genomic DNA library, cloned in the bacteriophage vector Charon 4A, was screened for HRG gene using a full-length cDNA coding for human IMI as a probe. A total of 7 clones were isolated from 6 × 105 phage and each was plaque purified. The entire HRG gene is represented in 3 genomic inserts with overlapping sequences that carry human DNA spanning 30 kb. Overlapping gene fragments were subcloned into pUC9 and characterized by Southern blot hybridization using 5’ and 3’ end probes isolated from human HRG cDNA and by DNA sequencing. These studies have shown that the gene for human HRG spans about 9 kb and consists of at least 5 exons and 4 introns. The putative histidine-rich region consisted of 12 tandemly repeated sequences of a 5 amino acid segment and 2 proline-rich regions contiguous to it are likely to be involved within one exon.