Translation of thyroglobulin 33S messenger RNA as a means of determining thyroglobulin quaternary structure

Thyroglobulin is a 19S protein of approximately 660,000 daltons and unknown quaternary structure. We have previously shown that a 33S mRNA purified from mammalian thyroids promoted synthesis in the Xenopus oocyte of a peptide immunologically related to thyroglobulin. Chemical identity to the native protein is now presented by means of a tryptic peptide analysis. Moreover, the 33S mRNA is shown to contain all the information required for the synthesis of a complete 19S thyroglobulin molecule. Gel filtration in Sepharose under denaturing conditions indicates that the reduced polypeptide encoded by the 33S mRNA is larger than 210,000 daltons. A model of a dimeric thyroglobulin with about 300,000 dalton subunits is presented.