Nucleotide sequence of the haptoglobin and haptoglobin-related gene pair. The haptoglobin-related gene contains a retrovirus-like element.

Thirty-three kilobase pairs (kb) of human DNA containing the haptoglobin (Hp) and haptoglobin-related (Hpr) gene pair were cloned, and the nucleotide sequence of 21-kb DNA was determined. The two genes are closely linked, with Hpr being 2.2 kb downstream of Hp. Six hundred nucleotides of DNA occur between the two genes that are not found either 5' to the Hp gene or 3' to the Hpr gene. After the duplication event, the first intron of the Hpr gene acquired a 9-kb insert consisting mainly of a retrovirus-like element with a potential primer-binding site homologous to a mouse isoleucine tRNA. The element forms a repeated family in the human genome that I name RTVL-I (retrovirus-like element-isoleucine). In the coding region of the Hpr gene, there are no frameshift or nonsense mutations and its exon-intron splicing sites, 5' flanking and 3' flanking sequences do not show any obvious defects. There are 28 amino acid differences between the decoded amino acid sequences of the Hpr and Hp genes. Sixteen of these differences occur in the hpr beta chain, and all appear to be located on the surface of the molecule in places not thought to be involved in the hemoglobin binding function of haptoglobin. The structure of the Hpr gene suggests that the gene may be expressed and give rise to a functional product.