The biosynthesis of bovine fibrinogen, prothrombin, and albumin in a cell-free system.

Preparative amounts of poly A-containing mRNA were isolated from bovine liver. In the presence of a cell-free system from rabbit reticulocytes, this mRNA stimulated the synthesis of a number of plasma proteins including albumin, fibrinogen, prothrombin, and antithrombin III. Automatic Edman degradation of immunoprecipitated albumin showed that this protein was synthesized as preproalbumin containing an NH2-terminal extension of 18 amino acid residues. Prothrombin is also synthesized as a precursor (preprothrombin), and the signal sequence for this protein is also rich in hydrophobic amino acids. The three chains of fibrinogen are synthesized from individual mRNAs, which are then linked by disulfide bonds to form the mature protein.