Biosynthesis of rabbit haptoglobin: Chemical evidence for a single chain precursor

Abstract
The primary translation product of the mRNA for rabbit haptoglobin was obtained from a rabbit reticulocyte lysate cell‐free system by immunoprecipitation with an antiserum that was directed to the β chain of haptoglobin. Analysis of the translation product by gel electrophoresis and by protein sequencing analysis identified a single polypeptide of M r 41 000. Sequence analysis established a signal region of 18 residues that was immediately followed by the α chain sequence. These results give strong evidence that haptoglobin is initially synthesized as a single chain composed of a signal peptide followed by α and β chain regions, respectively.