Molecular cloning and sequencing of the cDNA of rat alpha 1-protease inhibitor and its expression in COS-1 cells.

A cDNA clone for alpha 1-protease inhibitor (pc alpha 1P1212) was isolated from a lambda ZAP rat liver cDNA library. The 1.4 kb cDNA insert of pc alpha 1P1212 contained an open reading frame that encodes a 411-residue polypeptide (46,125 Da), in which a signal peptide of 24 residues was identified by comparison with the NH2-terminal sequence of the purified protein. Three potential sites for N-linked glycosylation were found in the molecule, accounting for the difference in molecular mass between the predicted form and the purified protein (56 kDa). The deduced primary structure of rat alpha 1-protease inhibitor showed 68.5% homology to that of the human inhibitor. We then constructed the expression plasmid pSV2 alpha 1PI from pSV2-gpt and pc alpha 1P1212, and transfected it into COS-1 cells. The transfected cells synthesized a molecule which was precipitated with anti-(rat alpha 1-protease inhibitor)-IgG and had the same molecular size as that of the inhibitor produced by rat hepatocytes.