PROTEIN-SYNTHESIS BY RAT TRANSPLANTABLE YOLK-SAC TUMOR AND ITS RELATION TO CYTOSOL LEVELS OF TRANSLATABLE MESSENGER-RNAS

Abstract

.alpha.-Fetoprotein (AFP) was the major secretory protein produced in vitro by normal rat yolk sacs. While not so active, AFP production was also detected in the transplantable tumors derived from normal yolk sacs. The major secretory protein synthesized by the tumor cells had a MW of 40,000 and was reactive with an anti-rat albumin antibody. The functional mRNA coding for these proteins was quantitated by translation in a cell-free system derived from wheat germ followed by specific immunoprecipitation of the newly synthesized peptides. The overall template activity of the RNA prepared from the normal yolk sacs and yolk sac tumor cells was virtually identical. The cytosol RNA prepared from the normal yolk sacs was approximately 12 times more active than that from the tumor cells in directing the synthesis of AFP. The presence of the cytosol RNA prepared from the tumor cells was required for the synthesis of proteins immunoprecipitable with the antialbumin antibody. The changes in AFP and albumin synthesis apparently can be accounted for by a corresponding change in the levels of functional mRNA coding for these proteins.