MGA2 or SPT23 Is Required for Transcription of the 9 Fatty Acid Desaturase Gene, OLE1, and Nuclear Membrane Integrity in Saccharomyces cerevisiae

Corresponding author: David J. Garfinkel, Movable Genetic Elements Section, Gene Regulation and Chromosome Biology Laboratory, ABL-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, P.O. Box B, Frederick, MD 21702-1201., garfinke{at}mail.ncifcrf.gov (E-mail)

Communicating editor: F. WINSTON

MGA2 and SPT23 are functionally and genetically redundant homologs in Saccharomyces cerevisiae. Both genes are implicated in the transcription of a subset of genes, including Ty retrotransposons and Ty-induced mutations. Neither gene is essential for growth, but mga2 spt23 double mutants are inviable. We have isolated a gene-specific activator, SWI5, and the 9 fatty acid desaturase of yeast, OLE1, as multicopy suppressors of an mga2 spt23 temperature-sensitive mutation (spt23-ts). The level of unsaturated fatty acids decreases 35–40% when the mga2 spt23-ts mutant is incubated at 37°. Electron microscopy of these cells reveals a separation of inner and outer nuclear membranes that is sometimes accompanied by vesicle-like projections in the intermembrane space. The products of Ole1p catalysis, oleic acid and palmitoleic acid, suppress mga2 spt23-ts and mga2 spt23 lethality and restore normal nuclear membrane morphology. Furthermore, the level of the OLE1 transcript decreases more than 15-fold in the absence of wild-type Mga2p and Spt23p. Our results suggest that Mga2p/Spt23p control cell viability by stimulating OLE1 transcription.

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