The karyogamy gene KAR2 and novel proteins are required for ER-membrane fusion.
We have developed assays using cells and isolated membranes to identify factors mediating fusion of the ER-nuclear membrane network in yeast. When cells containing distinctly tagged ER-nuclear envelope membranes are observed during mating, the markers of both parental membranes become colocalized in a process sharing a genetic requirement with karyogamy. Using isolated membranes, we find that fusion between ER compartments requires ATP, but not cytosol, Sec17p (alpha-SNAP), or Sec18p (NSF), the latter two being required at the fusion step in vesicular transport. Proteins tightly associated with the ER membrane are essential for fusion, as is Kar2p (BiP), an ER lumenal hsp70 homolog. BiP may activate an ER-localized fusogen, allowing nuclear fusion and karyogamy in yeast.
Latterich
M
M
Howard Hughes Medical Institute, University of California, Berkeley 94720.
Schekman
R
R
D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate / Q000378:metabolism; D001681:Biological Assay / Q000379:methods; D015415:Biomarkers; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003433:Crosses, Genetic; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005800:Genes, Fungal / Q000502:physiology*; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D008561:Membrane Fusion / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009685:Nuclear Envelope / Q000378:metabolism*; D019704:Protein Disulfide-Isomerases; D011498:Protein Precursors / Q000378:metabolism; D000069816:SEC Translocation Channels; D029701:Saccharomyces cerevisiae Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D033921:Vesicular Transport Proteins; D015003:Yeasts / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D015053:Zygote / Q000502:physiology
D015415:Biomarkers; D002352:Carrier Proteins; D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C060153:KAR2 protein, yeast; D008565:Membrane Proteins; D011498:Protein Precursors; D000069816:SEC Translocation Channels; C075137:SEC17 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D033921:Vesicular Transport Proteins; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C064404:SEC18 protein, S cerevisiae; C076879:EUG1 protein, S cerevisiae; D019704:Protein Disulfide-Isomerases