The yeast gene ERG6 is required for normal membrane function but is not essential for biosynthesis of the cell-cycle-sparking sterol.
In Saccharomyces cerevisiae, methylation of the principal membrane sterol at C-24 produces the C-28 methyl group specific to ergosterol and represents one of the few structural differences between ergosterol and cholesterol. C-28 in S. cerevisiae has been suggested to be essential for the sparking function (W. J. Pinto and W. R. Nes, J. Biol. Chem. 258:4472-4476, 1983), a cell cycle event that may be required to enter G1 (C. Dahl, H.-P. Biemann, and J. Dahl, Proc. Natl. Acad. Sci. USA 84:4012-4016, 1987). The sterol biosynthetic pathway in S. cerevisiae was genetically altered to assess the functional role of the C-28 methyl group of ergosterol. ERG6, the putative structural gene for S-adenosylmethionine: delta 24-methyltransferase, which catalyzes C-24 methylation, was cloned, and haploid strains containing erg6 null alleles (erg6 delta 1 and erg6 delta ::LEU2) were generated. Although erg6 delta cells are unable to methylate ergosterol precursors at C-24, they exhibit normal vegatative growth, suggesting that C-28 sterols are not essential in S. cerevisiae. However, erg6 delta cells exhibit pleiotropic phenotypes that include defective conjugation, hypersensitivity to cycloheximide, resistance to nystatin, a severely diminished capacity for genetic transformation, and defective tryptophan uptake. These phenotypes reflect the role of ergosterol as a regulator of membrane permeability and fluidity. Genetic mapping experiments revealed that ERG6 is located on chromosome XIII, tightly linked to sec59.
Gaber
R F
RF
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208.
Copple
D M
DM
Kennedy
B K
BK
Vidal
M
M
Bard
M
M
D001692:Biological Transport; D003001:Cloning, Molecular; D003227:Conjugation, Genetic; D004252:DNA Mutational Analysis; D004875:Ergosterol / Q000378:metabolism*; D005800:Genes, Fungal; D008563:Membrane Lipids / Q000235:genetics* / Q000378:metabolism; D008780:Methyltransferases / Q000032:analysis / Q000235:genetics*; D010957:Plasmids; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D014170:Transformation, Genetic; D014364:Tryptophan / Q000378:metabolism
D008563:Membrane Lipids; D014364:Tryptophan; D008780:Methyltransferases; C022670:delta 24-sterol methyltransferase; D004875:Ergosterol