Molecular cloning of the 8000-base thyroglobulin structural gene

Bovine thyroglobulin mRNA was reverse-transcribed into full-length double-stranded cDNA. The existence of three HindIII restriction endonuclease sites in the 8000-base thyroglobulin structural gene had allowed the easy cloning of the two internal HindIII fragments [Christophe et al. (1980) Eur. J. Biochem. 111, 419-423]. In the present study, the central portion of the structural gene was cloned in Escherichia coli as two individual recombinant plasmids containing 2000-base-pair and 4700-base-pair segments located respectively 5' and 3' relative to the unique BamHI site of the cDNA. BamHI linkers were added to the double-stranded cDNA and, following restriction with HindIII, selective cloning of the 5' (2600-base-pair) and 3' (1000-base-pair) terminal HindIII fragments was achieved by inserting them between the HindIII and BamHI sites of the plasmid pBR322. Partial sequencing of the 1000-base-pair 3'-terminal fragment demonstrated the presence of an A-A-U-A-A-A sequence in the mRNA 14 bases upstream from a poly(A) tract corresponding to the 3' end of the mRNA. Together, the four clones represent about 99% of the thyroglobulin structural gene and provide the starting material for the determination of thyroglobulin primary structure.