The role of structural signals in intercompartmental transport has been addressed by the isolation of yeast invertase (SUC2) mutations that cause intracellular accumulation of active enzyme. Two mutations that delay transport of core-glycosylated invertase, but not acid phosphatase, have been mapped in the 5' coding region of SUC2. Both mutations reduce specifically the transport of invertase to a compartment, presumably in the Golgi body, where outer chain carbohydrate is added. Subsequent transport to the cell surface is not similarly delayed. One mutation (SUC2-sl) converts an ala codon to val at position -1 in the signal peptide; the other (SUC2-s2) changes a thr to an lie at position +64 in the mature protein.Mutation sl results in about a 50-fold reduced rate of invertase transport to the Golgi body which is attributable to defective signal peptide cleavage. While peptide cleavage normally occurs at an ala-ser bond, the sl mutant form is processed slowly at the adjacent ser-met position giving rise to mature invertase with an N-terminal met residue, s2 mutant invertase is transported about sevenfold more slowly than normal, with no delay in signal peptide cleavage, and no detectable abnormal physical property of the enzyme. This substitution may interfere with the interaction of invertase and a receptor that facilitates transport to the Golgi body.The compartmentation of eucaryotic cells implies both specific mechanisms for protein localization and identifying signals that are recognized by the localization apparatus. Protein transport must be targeted not only to distinct organelles but to specific subdivisions within such organelles as the mitochondrion, chloroplast, endoplasmic reticulum (ER), ~ Golgi body, and plasma membrane. This process probably involves a number of unique identifying signals of which only a few have been deciphered. Clearly distinct N-terminal signal peptides direct secretory, mitochondrial, and chloroplast precursors to their respective organelles (1-3); hydrophobic membrane anchoring sequences have been recognized in viral glycoproteins (4, 5) and surface-bound immunoglobulin (6); a cytoplasmic, C-terminal peptide has been implicated in rapid transport of vesicular stomatitis virus G protein from the ER (7); and oligosaccharide phosphorylation triggers the t Abbreviations used in this paper." E and I fractions, external and intraceilular fractions; endo H, endoglycosidase H; ER, endoplasmic reticulum; YPD medium, 1% Bacto-Yeast extract, 2% Bacto-peptone, and 2% glucose (YP medium, same but without glucose).
The soluble protein patterns and electrophoretic mobilities of malate and succinate dehydrogenases and catalase have been examined in 25 strains of Propionibacterium acnes, P. granulosum, and P. avidum. A distinctive protein pattern for each species was found, and it was possible also to distinguish the serotypes within P. acnes and P. avidum. Strains of P. acnes, P. granulosum, and P. avidum could be differentiated by the mobilities of their malate dehydrogenases. Catalase activity was detected in the soluble fractions of all strains. Catalases from P. acnes and P. avidum strains had the same mobility, whereas that from P. granulosum was slightly slower. Under the conditions used, succinate dehydrogenase activity could be detected, but the patterns were not distinctive.
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