The alpha2 cDNA sequence of human haptoglobin carries a bacterial promoter functional in vivo
Various constructions of human haptoglobin (Hp) cDNA coding either for the complete alpha2FSbeta precursor protein or only for the beta subunit have been placed under the control of the Î»PR 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 alpha2FSbeta constructions constitutively express a smaller polypeptide of approx 30,000 dalton corresponding to a truncated Hp protein. Computer analysis of the HpcDNA revealed the presence of two strong potential bacterial promoters (alpha2PF and alpha2PS) located in the duplicated alpha2FS 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 Hpalpha2 cDNA sequence, when fused upstream to the cDNA coding for alpha1-antitrypsin, constitutively promotesin vivo the efficient expression of an hybrid protein specifically recognized by antibodies raised against alpha1-antitrypsin or haptoglobin.