Inhibition of acetyl coenzyme a carboxylase activity restores expression of the INO1 gene in a snf1 mutant strain of Saccharomyces cerevisiae

Mutations in the Saccharomyces cerevisiae SNF1 gene affect a number of cell ular processes, including the expression of genes involved in carbon source utilization and phospholipid biosynthesis. To identify targets of the Snf1 kinase that modulate expression of INO1, a gene required for an early, rat e-limiting step in phospholipid biosynthesis, we performed a genetic select ion for suppressors of the inositol auxotrophy of snf1 Delta strains. We id entified mutations in ACC1 and FAS1, two genes important for fatty acid bio synthesis in yeast; ACC1 encodes acetyl coenzyme A carboxylase (Acc1), and FAS1 encodes the beta subunit of fatty acid synthase. Acc1 was shown previo usly to be phosphorylated and inactivated by Snf1. Here we show that snf1 D elta strains with increased Acc1 activity exhibit decreased INO1 transcript ion. Strains carrying the ACC1 suppressor mutation have reduced Acc1 activi ty in vitro and in vivo, as revealed by enzymatic assays and increased sens itivity to the Acc1-specific inhibitor soraphen A. Moreover, a reduction in Acc1 activity, caused by addition of soraphen A, provision of exogenous fa tty acid, or conditional expression of ACC1, suppresses the inositol auxotr ophy of snf1 Delta strains. Together, these findings indicate that the inos itol auxotrophy of snf1 Delta strains arises in part from elevated Acc1 act ivity and that a reduction in this activity restores INO1 expression in the se strains. These results reveal a Snf1-dependent connection between fatty acid production and phospholipid biosynthesis, identify Acc1 as a Snf1 targ et important for INO1 transcription, and suggest models in which metabolite s that are generated or utilized during fatty acid biosynthesis can signifi cantly influence gene expression in yeast.