Phosphatidylinositol 3-phosphate 5-kinase is required for the cellular response to nutritional starvation and mating pheromone signals in Schizosaccharomyces pombe.
BACKGROUND
Phosphatidylinositol (3,5) bisphosphate, which is converted from phosphatidylinositol 3-phosphate by phosphatidylinositol 3-phosphate 5-kinase, is implicated in vacuolar functions and the sorting of cell surface proteins within endosomes in the endocytic pathway of budding yeast. A homologous protein, SpFab1p, has been found in the fission yeast Schizosaccharomyces pombe, but its role is not known.


RESULTS
Here we report that SpFab1p is encoded by ste12+ known as a fertility gene in S. pombe. The ste12 mutant grew normally under stress-free conditions, but was highly vacuolated and swelled at high temperatures and under starvation conditions. In nitrogen-free medium, ste12 cells were arrested in G1 phase, but partially defective in the expression of genes responsible for mating and meiosis. The ste12 mutant was defective both in the production of, and in the response to, mating pheromones. The amount of the pheromone receptor protein Map3p, was substantially decreased in ste12 cells. Map3p was transported to the cell surface, then internalized and eventually transported to the vacuolar lumen, even in the ste12 mutant.


CONCLUSIONS
The results indicate that phosphatidylinositol(3,5)bisphosphate is essential for cellular responses to various stresses and for the mating pheromone signalling under starvation conditions.
Morishita
Masayo
M
Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan.
Morimoto
Fusako
F
Kitamura
Kenji
K
Koga
Takako
T
Fukui
Yasuhisa
Y
Maekawa
Hiromi
H
Yamashita
Ichiro
I
Shimoda
Chikashi
C
D000595:Amino Acid Sequence; D003470:Culture Media; D005656:Fungal Proteins / Q000235:genetics; D008540:Meiosis / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000378:metabolism* / Q000502:physiology; D016415:Sequence Alignment; D012724:Sex Attractants / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics
D003470:Culture Media; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D012724:Sex Attractants; D014157:Transcription Factors; C095504:FAB1 protein, S cerevisiae; D017853:Phosphotransferases (Alcohol Group Acceptor)