Topology of membrane insertion in vitro and plasma membrane assembly in vivo of the yeast arginine permease

Abstract

We have examined the topology of the yeast arginine permease, a plasma‐membrane protein with multiple membrane‐spanning domains. Using fusions of the permease with the glycosylatable secreted yeast protein, acid phosphatase, we identified membrane‐spanning sequences that can translocate adjacent acid phosphatase across the membrane of the endoplasmicreticulum (ER), as measured by in vitro glycosylation. Examination for the presence or absence ofglycosylation in a systematic series of such fusions gave an internally consistent model for the lumenat orcytoplasmic disposition of the acid phosphatase reporter, defining the topology of the permease. The phenotypes of a further set of arginine permease gene fusions with portions of the gene for the secreted protein, killer toxin, suggest that the pathways of export of membrane and secreted proteins need not be functionally distinct.