Transferrin (Tf) is the major iron binding protein in vertebrate serum. It shares homologous amino acid sequences with four other proteins: lactotransferrin, ovotransferrin, melanoma antigen p97, and HuBlym-l. Antigen p97 and the Tf receptor genes have been mapped on human chromosome 3. The goal of the study described here was to initiate the characterization of the Tf gene by identifying and characterizing its cDNA and mapping its chromosomal location. Recombinant plasmids containing human cDNA encoding Tf have been isolated by screening an adult human liver library with a mixed oligonucleotide probe. Within the 2.3 kilobase pairs of TfcDNA analyzed, there is a probable leader sequence encoded by 57 nucleotides followed by 2037 nucleotides that encode the homologous amino and carboxyl domains. During evolution, three areas of the homologous amino and carboxyl domains have been strongly conserved, possibly reflecting functional constraints associated with iron binding. Chromosomal mapping by in situ hybridization and somatic cell hybrid analysis indicate that the Tfgene is located at q21-25 on human chromosome 3, consistent with linkage of the Tf, Tf receptor, and melanoma p97 loci.Transferrin (Tf) carries ferric iron from the intestine, reticuloendothelial system, and liver parenchymal cells to all proliferating cells in the body. The family of Tf-like proteins represents the product of an intragenic duplication followed by a series of independent gene duplications (1-4). Serum Tf (1), hen ovotransferrin (2, 3), lactotransferrin (4), melanoma antigen p97 (5), and a transforming protein from chicken lymphoma ChBlym-1 (6) share strong amino acid sequence homologies. A transforming protein from Burkitt lymphomas recently described (7) may also belong to the Tf family. There is also significant internal homology in the amino-terminal (NH2) and carboxyl-terminal (COOH) domains of Tf, lactotransferrin, and ovotransferrin (1-4). For example, the NH2 and COOH domains of human Tf reveal 40% identity when the NH2 domain (residues 1-336) and the COOH domain (residues 337-678) are compared (1). In the study described Screening of cDNA Clones. The cDNA library, kindly provided by Stuart H. Orkin (Harvard Medical School, Boston) was constructed from human liver RNA as described (10). The cDNA library was incubated overnight on L agar plates containing 10 jig of tetracycline per ml and was transferred to nitrocellulose filters. The plasmids were amplified with 250 ,tg of chloramphenicol per ml and the filters were prepared for hybridization as described by Grunstein and Hogness (11). The filters were hybridized at 37°C with 32P-labeled oligonucleotide mixed probes as described by Wallace, et al. (12). The hybridization mixture contained 0.9 M NaCl, 0.09 M Tris HCl (pH 7.5), 0.006 M EDTA, 0.5% NaDodSO4, Denhardt's (13) solution (5 x strength), 100 ,ug of denatured Escherichia coli DNA per ml, and 6.4 ng of 5' end-labeled oligonucleotide mixed probes per ml having a specific activity of -7 x 108 cpm/,ug.Preparation...

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.