CLONING AND CHARACTERIZATION OF CDNA FOR INTER-ALPHA-TRYPSIN INHIBITOR FAMILY HEAVY CHAIN-RELATED PROTEIN (IHRP), A NOVEL HUMAN PLASMA GLYCOPROTEIN

The cDNA encoding inter-alpha-trypsin inhibitor family heavy chain-rel ated protein (IHRP) was cloned from human liver cDNA libraries, Oligon ucleotide primers of human liver cDNA for PCR were constructed from in ternal amino acid sequences obtained with proteolytic fragments of IHR P. The amplified cDNA served as a hybridization probe for the screenin g of human liver cDNA libraries, The cDNA of 2,977 bp contained an ent ire reading frame coding 930 amino acids. The N-terminal 28 residues c orresponded to a signal peptide for secretion, The N-terminal 600 resi dues of the mature form exhibited considerable homology to those of IT I heavy chains, while the C-terminal 300 residues showed no homology w ith the heavy chains and low homology with ATP-dependent proteases. IH RP was readily cleaved into 85- and 35-kDa fragments when plasma was i ncubated at 37 degrees C. The cleaved site, Arg-Arg-Leu, was within a proline-rich region, Northern blot analysis of poly(A) RNAs from vario us human tissues only showed hybridization to liver RNA.