O-Glycosylation of Axl2/Bud10p by Pmt4p is required for its stability, localization, and function in daughter cells.
Cells of the yeast Saccharomyces cerevisiae choose bud sites in a manner that is dependent upon cell type: a and alpha cells select axial sites; a/alpha cells utilize bipolar sites. Mutants specifically defective in axial budding were isolated from an alpha strain using pseudohyphal growth as an assay. We found that a and alpha mutants defective in the previously identified PMT4 gene exhibit unipolar, rather than axial budding: mother cells choose axial bud sites, but daughter cells do not. PMT4 encodes a protein mannosyl transferase (pmt) required for O-linked glycosylation of some secretory and cell surface proteins (Immervoll, T., M. Gentzsch, and W. Tanner. 1995. Yeast. 11:1345-1351). We demonstrate that Axl2/Bud10p, which is required for the axial budding pattern, is an O-linked glycoprotein and is incompletely glycosylated, unstable, and mislocalized in cells lacking PMT4. Overexpression of AXL2 can partially restore proper bud-site selection to pmt4 mutants. These data indicate that Axl2/Bud10p is glycosylated by Pmt4p and that O-linked glycosylation increases Axl2/ Bud10p activity in daughter cells, apparently by enhancing its stability and promoting its localization to the plasma membrane.
Sanders
S L
SL
Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143-0448, USA. sylvias@mit.edu
Gentzsch
M
M
Tanner
W
W
Herskowitz
I
I
D000581:Amidohydrolases / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D016764:Cell Polarity / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D005656:Fungal Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D005800:Genes, Fungal / Q000235:genetics / Q000502:physiology; D006031:Glycosylation / Q000187:drug effects; D006056:Golgi Apparatus / Q000378:metabolism; D008364:Mannosyltransferases / Q000235:genetics / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008970:Molecular Weight; D009154:Mutation; D009844:Oligosaccharides / Q000378:metabolism; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase; D010641:Phenotype; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014415:Tunicamycin / Q000494:pharmacology
C098775:Axl2 protein, S cerevisiae; D005656:Fungal Proteins; D008562:Membrane Glycoproteins; D009844:Oligosaccharides; D029701:Saccharomyces cerevisiae Proteins; D014415:Tunicamycin; D008364:Mannosyltransferases; C082696:protein O-mannosyltransferase; D000581:Amidohydrolases; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase