The karyogamy gene KAR2 and novel proteins are required for ER-membrane fusion.
basic_science · Level V
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Abstract
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.
Medical subject headings
- Adenosine Triphosphatases
- Endoplasmic Reticulum
- Fungal Proteins
- Genes, Fungal
- HSP70 Heat-Shock Proteins
- Heat-Shock Proteins
- Membrane Fusion
- Nuclear Envelope
- Protein Disulfide-Isomerases
- Saccharomyces cerevisiae Proteins
- Vesicular Transport Proteins