Yeast KEX1 protease cleaves a prohormone processing intermediate in mammalian cells.

A vaccinia virus vector was used to express the yeast KEX1 gene, which encodes a prohormone carboxypeptidase specific for the removal of basic amino acids from prohormone processing intermediates, in mammalian cells. When produced in BSC-40 cells, Kex1p was localized to the perinuclear region and conferred a large increase in enzymatic activity characteristic of this carboxypeptidase. Expression of the KEX1 gene together with the yeast KEX2 gene, which encodes a prohormone endopeptidase specific for cleavage at pairs of basic amino acids, and the mouse proopiomelanocortin (mPOMC) cDNA in BSC-40 cells resulted in the full conversion of mPOMC to mature peptides including gamma-lipotropin. This in vivo processing of mPOMC to mature peptides by the KEX2/KEX1 gene products demonstrates a significant functional homology of the basic prohormone processing machinery in yeast and neuroendocrine cells.