Translocation in yeast and mammalian cells: not all signal sequences are functionally equivalent.
In Saccharomyces cerevisiae, nascent carboxypeptidase Y (CPY) is directed into the endoplasmic reticulum by an NH2-terminal signal peptide that is removed before the glycosylated protein is transported to the vacuole. In this paper, we show that this signal peptide does not function in mammalian cells: CPY expressed in COS-1 cells is not glycosylated, does not associate with membranes, and retains its signal peptide. In a mammalian cell-free protein-synthesizing system, CPY is not translocated into microsomes. However, if the CPY signal is either mutated to increase its hydrophobicity or replaced with that of influenza virus hemagglutinin, the resulting precursors are efficiently translocated both in vivo and in vitro. The implications of these results for models of signal sequence function are discussed.
Bird
P
P
Department of Biochemistry, University of Texas Health Center, Dallas 75235.
Gething
M J
MJ
Sambrook
J
J
D000818:Animals; D001692:Biological Transport; D002268:Carboxypeptidases / Q000378:metabolism*; D043402:Cathepsin A; D002460:Cell Line; D002522:Chlorocebus aethiops; D004252:DNA Mutational Analysis; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006389:Hemagglutinins, Viral / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D012995:Solubility; D013329:Structure-Activity Relationship
D006389:Hemagglutinins, Viral; D021382:Protein Sorting Signals; D029701:Saccharomyces cerevisiae Proteins; D002268:Carboxypeptidases; D043402:Cathepsin A; C499283:PRC1 protein, S cerevisiae; C022633:serine carboxypeptidase