Structural and immunological identity of rat hepatoma and fetal liver nuclear poly(A) polymerase

Poly(A) polymerase was partially purified from isolated nuclei of fetal rat liver. Antibodies produced in rabbits immunized with purified nuclear poly(A) polymerase from a rat hepatoma exhibited nearly identical affinity for the partially purified fetal liver and hepatoma enzymes. The extent of the antibody reaction with adult liver nuclear poly(A) polymerase partially purified in a similar manner was only 1.4% of that obtained with the hepatoma enzyme. Immune complex formation was observed between the antibodies and a major polypeptide in the fetal liver enzyme preparation which corresponded to the hepatoma enzyme (mol. wt. 48 000). No other polypeptide in the fetal liver enzyme preparation reacted with the antibodies. The 48-kDa fetal liver polypeptide produced a CNBr cleavage pattern identical to that of hepatoma poly(A) polymerase which is known to be different from the cleavage pattern of the adult liver major nuclear poly(A) polymerase. A fetal liver polypeptide corresponding to the adult liver enzyme (mol. wt. 38 000) was not evident. These results coupled with other data suggest that the hepatoma nuclear poly(A) polymerase is an oncofetal protein.