Human group-specific component (Gc) is a member of the albumin family.

The group-specific component (Gc) is the major vitamin D-binding protein in plasma. The gene encoding Gc is linked, on human chromosome 4, to the albumin and alpha-fetoprotein genes. These two genes previously were shown to have evolved from a smaller ancestral gene by intragenic triplication. Recombinant plasmids containing human cDNA encoding Gc have been isolated by screening an adult human liver library with a mixed oligonucleotide probe. Characterization of Gc cDNA has provided the complete amino acid sequence of the protein and revealed strong sequence homology with albumin and alpha-fetoprotein. Of particular interest is a conserved pattern of disulfide bridges that form the triple-domain structures in albumin, alpha-fetoprotein, and Gc. Gc cDNA was used as a probe in Southern blot analysis of somatic-cell hybrids to confirm that the Gc locus is on chromosome 4.

Evolution of haptoglobin: comparison of complementary DNA encoding Hp alpha 1S and Hp alpha 2FS.

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.

Localization of the haptoglobin alpha and beta genes (HPA and HPB) to human chromosome 16q22 by in situ hybridization.

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

Identification and characterization of human haptoglobin cDNA.

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 alpha 2-chain and beta-chain sequences. A heretofore unseen arginine residue was deduced between the human alpha- and beta-chain sequences. This is a probable site of limited proteolysis leading to the formation of the alpha and beta polypeptides in mature haptoglobin. A comparison of the haptoglobin alpha-beta-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 Hp alpha 2 gene, which was shown earlier to be a partial duplication produced by unequal crossing-over between Hp alpha 1 genes, has been impossible to align by protein characterization. The cDNA sequence establishes the alignment of Hp alpha 2FS in the Hp alpha 2 gene studied here.