Cloning and sequencing of liver cDNA coding for bovine protein C

cDNA coding for protein C has been cloned from a bovine liver library in plasmid vector pBR322 and its sequence has been determined. Two overlapping clones code for the entire light and heavy chains of the mature protein, as well as a previously unreported connecting dipeptide (Lys-Arg) and a 39-amino acid leader peptide region. Identification and characterization of the clones establishes the liver as a site of protein C biosynthesis. A contiguous coding region reveals that a one-chain precursor protein is made that upon limited proteolysis yields both the mature light and heavy chains. The codon for aspartic acid is found at light chain amino acid position 71, showing that the beta-hydroxyaspartic acid that exists in this position of the mature protein is the result of post-translational modification of an aspartic acid residue. Amino acid sequence homology in the amino-terminal region of the light chain with other vitamin K-dependent coagulation factors is continued into the leader peptide region.