Synthesis of high molecular weight thyroglobulin peptides by thyroid polysome in vitro.

Bovine thyroid polysomes were isolated under conditions which had yielded large polysomes in other systems. Between 25 and 40% of the protein synthesized by these polysomes could be precipitated by thyroglobulin antibody. When these immunoprecipitates were separated by dodecyl sulfate-polyacrylamide gel electrophoresis (4% running gel), over 50% of the radioactivity was located in the regions of polypeptides greater than 100,000 daltons. Between 11 and 13% of the total radioactivity was found as a single peak co-migrating with the main band of bovine thyroglobulin (Mr = 330,000). Peaks of radioactivity were also found in regions of molecular weights between 130,000 and 200,000. When the immunoprecipitates were separated in a 10% running gel, about 50% of the radioactivity was located in the top 8 mm of the gel. Most of the remaining radioactivity was distributed in regions corresponding to molecular weights greater than 68,000. No peak of radioactivity was seen corresponding to peptides of 15,000 daltons.