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Yeast cell surface growth is accomplished by constitutive secretion and plasma membrane assembly, culminating in the fusion of vesicles with the bud membrane. Coordination of secretion and membrane assembly has been investigated by examining the biogenesis of plasma membrane ATPase (PM ATPase) in secretion-defective (sec) strains of Saccharomyces cerevisiae. PM ATPase is synthesized as a approximately 106-kD polypeptide that is not detectably modified by asparagine-linked glycosylation or proteolysis during transit to the plasma membrane. Export of the PM ATPase requires the secretory pathway. In sec1, a mutant defective in the last step of secretion, large amounts of Golgi- derived vesicles are accumulated. Biochemical characterization of this organelle has demonstrated that PM ATPase and the secretory enzyme, acid phosphatase, are transported in a single vesicle species.