Molecular cloning of human haptoglobin cDNA: evidence for a single mRNA coding for alpha 2 and beta chains.
Human haptoglobin (Hp) is a plasma glycoprotein composed of alpha and beta polypeptide chains that are covalently associated by disulfide bonds. It had been suggested that alpha and beta polypeptides could be synthesized via a common precursor polypeptide. We report the molecular cloning of DNA complementary to human Hp mRNA. One of the clones, pULB1148, carries a full length copy coding for both alpha 2 and beta polypeptides. In vitro translation of human liver mRNA hybridizing with this cDNA gives a protein mol. wt. of 49000 daltons. The sequence of the alpha 2 beta cDNA shows the presence of a single Arg residue between Gln 142 of the alpha 2 chain and Ileu 1 of the beta chain. With a few minor exceptions, the DNA sequence fits the previously published amino acid sequences. The differences are the presence of an Asp residue at position 52 of alpha 2 instead of Asn, the existence in beta of only one Lys residue between Gly 65 and the following Gln, the presence of Ser and Cys at positions 218-219 instead of Cys-Ser, and of Asp residues at positions 205 and 235 instead of Asn.
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D006242:Haptoglobins / Q000235:genetics*; D006801:Humans; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism; D014176:Protein Biosynthesis; D011487:Protein Conformation; D012333:RNA, Messenger / Q000235:genetics*
D006242:Haptoglobins; D012333:RNA, Messenger; D004247:DNA