Molecular cloning of the large subunit of transforming growth factor type beta masking protein and expression of the mRNA in various rat tissues.

Masking protein (MP), which neutralizes the activity of transforming growth factor type beta 1 (TGF-beta 1), is composed of a dimeric N-terminal part of a TGF-beta 1 precursor of Mr 39,000 and an unknown large subunit of Mr 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 Mr of 186,596. The mature large subunit seems to be derived proteolytically from a prepro-precursor and the calculated Mr 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-beta 1 mRNA in various rat tissues.