Various constructions of human haptoglobin (Hp) cDNA coding either for the complete α2FSβ precursor protein or only for the β subunit have been placed under the control of the λPR promoter in the bacterial expression vector pCQV2 (Queen, 1983). In addition to the expected 45,000 dalton polypeptide synthesized after induction of the PR promoter, the complete α2FSβ constructions constitutively express a smaller polypeptide of ∼30,000 dalton corresponding to a truncated Hp protein. Computer analysis of the HpcDNA revealed the presence of two strong potential bacterial promoters (α2PF and α2PS) located in the duplicated α2FS sequence. Both Hp promoter signals are followed by potential mRNA start sites and ribosome binding sites at a compatible distance from initiation codons. In addition, the Hpα2 cDNA sequence, when fused upstream to the cDNA coding for α1-antitrypsin, constitutively promotes in vivo the efficient expression of an hybrid protein specifically recognized by antibodies raised against α1-antitrypsin or haptoglobin.

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