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.

Cloning and expression in Escherichia coli of full-length complementary DNA coding for human alpha 1-antitrypsin.

A cDNA library prepared from human liver was screened for alpha 1-antitrypsin, a major constituent of plasma which functions as inhibitor of proteolytic enzymes. The library was screened using a 12-base-long synthetic oligodeoxyribonucleotide corresponding to a known DNA fragment of human alpha 1-antitrypsin and by hybrid-selection of alpha 1-antitrypsin mRNA. A plasmid, pULB1523, was identified carrying a cDNA insert of about 1400 bp coding for human alpha 1-antitrypsin. Restriction mapping and DNA sequence analysis indicated that the 1400 bp code for the signal peptide and for the complete mature alpha 1-antitrypsin molecule. In addition, a solid-phase enzyme-linked immunoassay showed that pULB1523 expresses human alpha 1-antitrypsin in bacteria. Fusion of the alpha 1-antitrypsin sequence to the leader sequence of the beta-lactamase gene (plasmid pKT287) resulted also in the expression of the protein in bacteria.