UMMS Affiliation

Department of Molecular Genetics and Microbiology

Publication Date


Document Type



Adenosine Triphosphatases; Cell Membrane; DNA-Binding Proteins; Ethyl Methanesulfonate; Fungal Proteins; Gene Library; Genes, Reporter; Genetic Complementation Test; Genetic Vectors; Glycoside Hydrolases; Ligases; Membrane Proteins; Metalloendopeptidases; Models, Biological; Mutagenesis; Mutagens; Mutation; Phenotype; Plant Proteins; Precipitin Tests; Protein Binding; Protein Conformation; Protein Structure, Tertiary; Proteins; Recombinant Fusion Proteins; Saccharomyces cerevisiae; *Saccharomyces cerevisiae Proteins; Time Factors; *Ubiquitin-Conjugating Enzymes; beta-Fructofuranosidase; beta-Galactosidase; beta-Lactamases


Life Sciences | Medicine and Health Sciences


Yeast protein insertion orientation (PIO) mutants were isolated by selecting for growth on sucrose in cells in which the only source of invertase is a C-terminal fusion to a transmembrane protein. Only the fraction with an exocellular C terminus can be processed to secreted invertase and this fraction is constrained to 2-3% by a strong charge difference signal. Identified pio mutants increased this to 9-12%. PIO1 is SPF1, encoding a P-type ATPase located in the endoplasmic reticulum (ER) or Golgi. spf1-null mutants are modestly sensitive to EGTA. Sensitivity is considerably greater in an spf1 pmr1 double mutant, although PIO is not further disturbed. Pmr1p is the Golgi Ca(2+) ATPase and Spf1p may be the equivalent ER pump. PIO2 is STE24, a metalloprotease anchored in the ER membrane. Like Spf1p, Ste24p is expressed in all yeast cell types and belongs to a highly conserved protein family. The effects of ste24- and spf1-null mutations on invertase secretion are additive, cell generation time is increased 60%, and cells become sensitive to cold and to heat shock. Ste24p and Rce1p cleave the C-AAX bond of farnesylated CAAX box proteins. The closest paralog of SPF1 is YOR291w. Neither rce1-null nor yor291w-null mutations affected PIO or the phenotype of spf1- or ste24-null mutants. Mutations in PIO3 (unidentified) cause a weaker Pio phenotype, enhanced by a null mutation in BMH1, one of two yeast 14-3-3 proteins.

DOI of Published Version



Mol Biol Cell. 2002 Apr;13(4):1158-74. Link to article on publisher's site

Journal/Book/Conference Title

Molecular biology of the cell

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Link to Article in PubMed

PubMed ID