In vitro synthesis of rat fibrinogen: identification of preA alpha, preB beta, and pre gamma polypeptides.

Vertebrate fibrinogen consists of two sets of three nonidentical polypeptides that are synthesized in the liver. The subunits of fibrinogen have been synthesized in a cell-free, membrane-free translation system and compared with (alpha), polypeptides of fibrinogen purified from rat plasma and (b) subunits synthesized and secreted by hepatoma cells grown in culture. Rat hepatoma monolayers were grown with or without tunicamycin to prevent or allow glycosylation of the B beta and gamma subunits, respectively. Sodium dodecyl sulfate polyacrylamide gel analysis indicated that each of the polypeptides translated in vitro from mRNA is larger than its corresponding nonglycosylated fibrinogen chain. The primary translation A alpha, B beta, and gamma chains are larger than their authentic nonglycosylated counterparts by 600, 1100, and 3000 daltons, respectively. Furthermore, the preA alpha and preB beta translation products are thrombin sensitive. These results strongly imply that signal peptides exist on each of the primary translation products of fibrinogen.