Saccharomyces cerevisiae preferentially uses glucose as a carbon source, but
following its depletion, it can utilize a wide variety of other carbons including
nonfermentable compounds such as ethanol. A shift to a nonfermentable carbon
source results in massive reprogramming of gene expression including genes
involved in gluconeogenesis, the glyoxylate cycle, and the tricarboxylic acid cycle.
This review is aimed at describing the recent progress made toward understanding
the mechanism of transcriptional regulation of genes responsible for utilization of
nonfermentable carbon sources. A central player for the use of nonfermentable
carbons is the Snf1 kinase, which becomes activated under low glucose levels. Snf1
phosphorylates various targets including the transcriptional repressor Mig1,
resulting in its inactivation allowing derepression of gene expression. For example,
the expression of CAT8, encoding a member of the zinc cluster family of
transcriptional regulators, is then no longer repressed by Mig1. Cat8 becomes
activated through phosphorylation by Snf1, allowing upregulation of the zinc
cluster gene SIP4. These regulators control the expression of various genes
including those involved in gluconeogenesis. Recent data show that another zinc
cluster protein, Rds2, plays a key role in regulating genes involved in gluconeogenesis
and the glyoxylate pathway. Finally, the role of additional regulators such as
Adr1, Ert1, Oaf1, and Pip2 is also discussed.