Enhanced levels of Pis1p (phosphatidylinositol synthase) improve the growth of Saccharomyces cerevisiae cells deficient in Rsp5 ubiquitin ligase.
The Rsp5 ubiquitin ligase plays a role in many cellular processes including the biosynthesis of unsaturated fatty acids. The PIS1 (phosphatidylinositol synthase gene) encoding the enzyme Pis1p which catalyses the synthesis of phosphatidylinositol from CDP-diacyglycerol and inositol, was isolated in a screen for multicopy suppressors of the rsp5 temperature sensitivity phenotype. Suppression was allele non-specific. Interestingly, expression of PIS1 was 2-fold higher in the rsp5 mutant than in wild-type yeast, whereas the introduction of PIS1 in a multicopy plasmid increased the level of Pis1p 6-fold in both backgrounds. We demonstrate concomitantly that the expression of INO1 (inositol phosphate synthase gene) was also elevated approx. 2-fold in the rsp5 mutant as compared with the wild-type, and that inositol added to the medium improved growth of rsp5 mutants at a restrictive temperature. These results suggest that enhanced phosphatidylinositol synthesis may account for PIS1 suppression of rsp5 defects. Analysis of lipid extracts revealed the accumulation of saturated fatty acids in the rsp5 mutant, as a consequence of the prevention of unsaturated fatty acid synthesis. Overexpression of PIS1 did not correct the cellular fatty acid content; however, saturated fatty acids (C(16:0)) accumulated preferentially in phosphatidylinositol, and (wild-type)-like fatty acid composition in phosphatidylethanolamine was restored.
Kaliszewski
Pawel
P
Department of Genetics, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5a, 02-106 Warsaw, Poland.
Ferreira
Thierry
T
Gajewska
Beata
B
Szkopinska
Anna
A
Berges
Thierry
T
Zoładek
Teresa
T
D002384:Catalysis; D002470:Cell Survival; D056827:Endosomal Sorting Complexes Required for Transport; D005227:Fatty Acids / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D016153:Genes, Suppressor; D007294:Inositol / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D007296:Myo-Inositol-1-Phosphate Synthase / Q000235:genetics; D010641:Phenotype; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D013696:Temperature; D017855:Transferases (Other Substituted Phosphate Groups) / Q000235:genetics / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000172:deficiency* / Q000235:genetics; D015854:Up-Regulation / Q000235:genetics
D056827:Endosomal Sorting Complexes Required for Transport; D005227:Fatty Acids; D010714:Phosphatidylethanolamines; D010716:Phosphatidylinositols; D029701:Saccharomyces cerevisiae Proteins; C483858:phosphatidylethanolamine; D007294:Inositol; D043743:Ubiquitin-Protein Ligase Complexes; D017855:Transferases (Other Substituted Phosphate Groups); C478389:PIS1 protein, S cerevisiae; D007296:Myo-Inositol-1-Phosphate Synthase; C469287:RSP5 protein, S cerevisiae