Synthesis of very high molecular weight thyroglobulin in three heterologous systems.

Calf thyroid RNA has been translated in the wheat germ and messenger-dependent reticulocyte lysate cell free systems and in Xenopus laevis oocytes. Peptides immunologically related to and comigrating with 330 000 molecular weight thyroglobulin as well as both larger and smaller immunopeptides have been synthesized. The smaller molecular weight peptides were due at least in part to degradation during incubation despite the presence of protease inhibitors. The larger molecular weight peptides could represent degradation products of a single polypeptide chain with a molecular weight of 660 000. The 330 000 molecular weight peptides would then represent cleavage of the protomer into two subunits. To support this possibility, thyroid polysomal RNA large enough to code for a peptide with a molecular weight of 660 000 has been shown to be active in thyroglobulin synthesis and to maintain its integrity under denaturing conditions.