A novel fission yeast gene, tht1+, is required for the fusion of nuclear envelopes during karyogamy.
We have isolated a fission yeast karyogamy mutant, tht1, in which nuclear congression and the association of two spindle pole bodies occurs but the subsequent fusion of nuclear envelopes is blocked. The tht1 mutation does not prevent meiosis, so cells execute meiosis with two unfused nuclei, leading to the production of aberrant asci. The tht1(+) gene was cloned and sequenced. Predicted amino acid sequence has no significant homology to previously known proteins but strongly suggests that it is a type I membrane protein. The tht1(+) gene is dispensable for vegetative growth and expressed only in conjugating cells. Tht1p is a glycoprotein susceptible to endoglycosilase H digestion. Site- directed mutagenesis showed that the N-glycosylation site, as well as the COOH-terminal region of Tht1p, is essential for its function. A protease protection assay indicated that the COOH terminus is cytoplasmic. Immunocytological analysis using a HA-tagged Tht1p suggested that the protein is localized in nuclear envelopes and in the ER during karyogamy and that its levels are reduced in cells containing fused nuclei.
Tange
Y
Y
Kazusa DNA Research Institute, Kisarazu, Chiba 292, Japan.
Horio
T
T
Shimanuki
M
M
Ding
D Q
DQ
Hiraoka
Y
Y
Niwa
O
O
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics*; D015870:Gene Expression; D006023:Glycoproteins; D017404:In Situ Hybridization, Fluorescence; D050576:Membrane Fusion Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D009685:Nuclear Envelope / Q000502:physiology*; D010641:Phenotype; D012568:Schizosaccharomyces / Q000235:genetics* / Q000502:physiology; D029702:Schizosaccharomyces pombe Proteins; D013170:Spores
D005656:Fungal Proteins; D006023:Glycoproteins; D050576:Membrane Fusion Proteins; D029702:Schizosaccharomyces pombe Proteins; C110446:THT1 protein, S pombe