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Published May 1, 1988 | public
Journal Article Open

Intracellular sorting and processing of a yeast vacuolar hydrolase: proteinase A propeptide contains vacuolar targeting information


An inactive precursor form of proteinase A (PrA) transits through the early secretory pathway before final vacuolar delivery. We used gene fusions between the gene coding for PrA (PEP4) and the gene coding for the secretory enzyme invertase (SUC2) to identify vacuolar protein-sorting information in the PrA precursor. We found that the 76-amino-acid preprosegment of PrA contains at least two sorting signals: an amino-terminal signal peptide that is cleaved from the protein at the level of the endoplasmic reticulum followed by the prosegment which functions as a vacuolar protein-sorting signal. PrA-invertase hybrid proteins that carried this sequence information were accurately sorted to the yeast vacuole as determined by cell fractionation and immunolocalization studies. Hybrid proteins lacking all or a portion of the PrA prosegment were secreted from the cell. Our gene fusion data together with an analysis of the wild-type PrA protein indicated that N-linked carbohydrate modifications are not required for vacuolar sorting of this protein. Furthermore, results obtained with a set of deletion mutations constructed in the PrA prosegment indicated that this sequence also contributes to proper folding of this polypeptide into a stable transit-competent molecule.

Additional Information

Copyright © 1988 by the American Society for Microbiology. Received 26 October 1987; accepted 11 February 1988. We thank John DeModena for technical assistance, Michael W. Clark for advice on immunofluorescence techniques, and David Bedwell for critically reading the manuscript and helpful advice. This study was supported by Public Health Service grant GM 32703 from the National Institutes of Health to S.D.E. D.J.K. was supported by a research fellowship from the Helen Hay Whitney Foundation, and L.M.B. was supported by a graduate fellowship from the National Science Foundation.


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