The α² cDNA sequence of human haptoglobin carries a bacterial promoter functional in vivo

Various constructions of human haptoglobin (Hp) cDNA coding either for the complete α^2FSβ precursor protein or only for the β subunit have been placed under the control of the λP_R promoter in the bacterial expression vector pCQV2 (Queen, 1983). In addition to the expected 45,000 dalton polypeptide synthesized after induction of the P_R promoter, the complete α^2FSβ 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 (α²P_F and α²P_S) located in the duplicated α^2FS 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.