title: PHO5-LACZ hybrid proteins block translocation of native acid phosphatase in Saccharomyces cerevisiae.
abstract: A set of protein hybrids composed of variable portions of the amino-terminal residues of the yeast phosphate-repressible acid phosphatase (product of PHO5) and an active fragment of bacterial beta-galactosidase has been constructed. When these PHO5-LACZ hybrids are expressed in a yeast strain carrying an intact chromosomal PHO5 gene, they show a size-dependent interference with the secretion of native acid phosphatase. Hybrid proteins containing approximately 50 residues of acid phosphatase do not affect secretion of native acid phosphatase. Hybrids containing greater than 200 residues of acid phosphatase reduce the amount of secreted acid phosphatase more than by 50%. The interference with secretion is specific for acid phosphatase. The hybrids do not affect secretion of invertase, and do not confer a growth-deficient phenotype on yeast. Both the hybrid proteins and acid phosphatase accumulate in non-glycosylated, membrane-bound forms which are sensitive to proteolysis from the cytoplasmic side of the membrane. The hybrids and accumulated acid phosphatase co-migrate on Percoll density gradients with markers of the endoplasmic reticulum, but not with markers of the Golgi or secretory vesicles. These results suggest that PHO5-LACZ hybrid proteins specifically block secretion of native acid phosphatase by interfering with enzyme after targeting but before translocation across the endoplasmic reticulum.
mesh_terms: D000135:Acid Phosphatase / Q000096:biosynthesis / Q000235:genetics*; D004790:Enzyme Induction; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005696:Galactosidases / Q000235:genetics*; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism; D010957:Plasmids; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D043324:beta-Fructofuranosidase; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D000135:Acid Phosphatase; D005696:Galactosidases; D006026:Glycoside Hydrolases; D001616:beta-Galactosidase; D043324:beta-Fructofuranosidase