EXPRESSION OF A FUNCTIONAL THYROGLOBULIN FRAGMENT IN A BACULOVIRUS SYSTEM

The synthesis is described of an N-terminal thyroglobulin (Tg) polypep tide of 27 kDa, which is capable of hormonogenesis, in a baculovirus s ystem. This polypeptide was made using a 657 bp Tg cDNA cloned from hu man thyroid RNA by a polymerase chain reaction method. The cDNA contai ned the information for the Tg signal peptide, the N-terminally locate d site for thyroid hormone formation and, at the 3' end, a sequence co ding for six histidine residues. The fragments produced were purified using a nickel-nitrilotriacetic acid column using these six histidine residues. The products were analysed by sodium dodecyl sulphate-polyac rylamide gel electrophoresis and showed two glycosylated fragments of 32 and 34 kDa, both of which started with asparagine. Iodination of th e fragments with lactoperoxidase in vitro resulted in the formation of thyroxine (T-4). The formation rate of T-4 in the fragments was about five times lower than that of the mature Tg dimer of 660 kDa, but ten times more rapid than in bovine serum albumin under the same conditio ns.