Evolution of haptoglobin: comparison of complementary DNA encodingHpα1SandHpα2FS

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Abstract
Haptoglobin is a transport glycoprotein which removes free hemoglobin from the circulation of vertebrates. In human populations haptoglobin is polymorphic due to three alleles, Hpα1F, Hpα1S and Hpα2. The Hpα2 allele is roughly twice the length of the Hpα1 alleles and is the product of a partial gene duplication possibly resulting from an unequal crossover event in a heterozygous genotype Hpα1F/Hpα1S. In the study described here we compare the cDNA encoding Hpα1S to that encoding Hpα2FS. Both have a leader sequence followed by the genotypic α chain sequence, a β sequence and an untranslated sequence in the 3′ end. The cDNA encoding Hpα2FS is composed of α1F and α1S domains differing by four nucleotide replacements. Hpα1S cDNA contains the same replacement site mutations found in the α1S domain of Hpα2FS, indicating that this coding region has sustained few, if any, mutations since its incorporation into the Hpα2FS gene.