Immunolocalization of Kex2 protease identifies a putative late Golgi compartment in the yeast Saccharomyces cerevisiae.
The Kex2 protein of the yeast Saccharomyces cerevisiae is a membrane-bound, Ca2(+)-dependent serine protease that cleaves the precursors of the mating pheromone alpha-factor and the M1 killer toxin at pairs of basic residues during their transport through the secretory pathway. To begin to characterize the intracellular locus of Kex2-dependent proteolytic processing, we have examined the subcellular distribution of Kex2 protein in yeast by indirect immunofluorescence. Kex2 protein is located at multiple, discrete sites within wild-type yeast cells (average, 3.0 +/- 1.7/mother cell). Qualitatively similar fluorescence patterns are observed at elevated levels of expression, but no signal is found in cells lacking the KEX2 gene. Structures containing Kex2 protein are not concentrated at a perinuclear location, but are distributed throughout the cytoplasm at all phases of the cell cycle. Kex2-containing structures appear in the bud at an early, premitotic stage. Analysis of conditional secretory (sec) mutants demonstrates that Kex2 protein ordinarily progresses from the ER to the Golgi but is not incorporated into secretory vesicles, consistent with the proposed localization of Kex2 protein to the yeast Golgi complex.
Redding
K
K
Department of Biochemistry, Stanford University School of Medicine, California 94305.
Holcomb
C
C
Fuller
R S
RS
D002453:Cell Cycle; D003594:Cytoplasmic Granules / Q000201:enzymology; D004721:Endoplasmic Reticulum / Q000201:enzymology; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000201:enzymology*; D008938:Mitosis; D009154:Mutation; D043484:Proprotein Convertases; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D012697:Serine Endopeptidases / Q000032:analysis* / Q000276:immunology; D013381:Subtilisins; D013696:Temperature
D029701:Saccharomyces cerevisiae Proteins; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; D013381:Subtilisins; C058751:KEX2 protein, S cerevisiae