The group-specific component (Gc) is the

Recombinant plasmids containing human cDNA encoding haptoglobin, a plasma protein that binds free hemoglobin, have been isolated by screening an adult human liver library with a mixed oligonucleotide probe. Four cDNA clones containing inserts have been obtained .that span 1,218 nucleotides of the haptoglobin coding sequence, including the 3' end of the haptoglobin cDNA. The cDNA sequence included a leader sequence followed by a2-chain and fl-chain sequences. A heretofore unseen arginine residue was deduced between the human a-and fl-chain sequences. This is a probable site of limited proteolysis leading to the formation of the a and fi polypeptides in mature haptoglobin.A comparison of the haptoglobin a-p-junction region and the heavy-light-chain junction of tissue-type plasminogen activator strengthens the evolutionary homology found in haptoglobin and the serine proteases. The Hpa2 gene, which was shown earlier to be a partial duplication produced by unequal crossing-over between Hpal genes, has been impossible to align by protein characterization. The cDNA sequence establishes the alignment of Hpa2FS in the Hpa2 gene studied here.

Human haptoglobin (Hp) is a protein that binds free hemoglobin and circulates in plasma of vertebrates as a tetrachain (αβ)₂ structure. This study maps HPA and HPB, the genes encoding the Hp α and β chains to human chromosome band 16q22 by in situ hybridization.

Haptoglobin is a transport glycoprotein which removes free hemoglobin from the circulation of vertebrates. In human populations haptoglobin is polymorphic due to three alleles, Hp alpha 1F, Hp alpha 1S and Hp alpha 2. The Hp alpha 2 allele is roughly twice the length of the Hp alpha 1 alleles and is the product of a partial gene duplication possibly resulting from an unequal crossover event in a heterozygous genotype Hp alpha 1F/Hp alpha 1S. In the study described here we compare the cDNA encoding Hp alpha 1S to that encoding Hp alpha 2FS . Both have a leader sequence followed by the genotypic alpha chain sequence, a beta sequence and an untranslated sequence in the 3' end. The cDNA encoding Hp alpha 2FS is composed of alpha 1F and alpha 1S domains differing by four nucleotide replacements. Hp alpha 1S cDNA contains the same replacement site mutations found in the alpha 1S domain of Hp alpha 2FS , indicating that this coding region has sustained few, if any, mutations since its incorporation into the Hp alpha 2FS gene.

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