MOLECULAR-CLONING OF THE LARGE SUBUNIT OF TRANSFORMING GROWTH-FACTOR TYPE-BETA MASKING PROTEIN AND EXPRESSION OF THE MESSENGER-RNA IN VARIOUS RAT-TISSUES

Masking protein (MP), which neutralizes the activity of transforming growth factor type β1 (TGF-β1), is composed of a dimeric N-terminal part of a TGF-β1 precursor of M(r) 39,000 and an unknown large subunit of M(r) 105,000-120,000. The deduced primary structure of the MP large subunit was elucidated by determining the nucleotide sequence of its cDNA. The cDNA encodes a prepro-precursor of 1712 amino acid residues with a calculated M(r) of 186,596. The mature large subunit seems to be derived proteolytically from a prepro-precursor and the calculated M(r) is 91,606. The precursor has seven N-linked glycosylation sites and an unusual structure containing 18 epidermal growth factor-like domains and four cysteine-rich internal repeats. The large subunit mRNA is synthesized in parallel with the expression of TGF-β1 mRNA in various rat tissues.