Yeast KEX2 protease and mannosyltransferase I are localized to distinct compartments of the secretory pathway.

The KEX2 protease (product of the KEX2 gene) functions late in the secretory pathway of Saccharomyces cerevisiae by cleaving the polypeptide chains of prepro-killer toxin and prepro-alpha-factor at paired basic amino acid residues. The intracellular vesicles containing KEX2 protease sedimented in density gradients to a position distinct from those containing mannosyltransferase I (product of the MNN1 gene), a marker enzyme for the Golgi complex. The recovery of intact compartments containing these enzymes approached 80% after sedimentation. We propose that the KEX2 protease and mannosyltransferase I reside within distinct compartments.