Metabolic control of transcription: paradigms and lessons from Saccharomyces cerevisiae.

The comparatively simple eukaryote Saccharomyces cerevisiae is composed of some 6000 individual genes. Specific sets of these genes can be transcribed co-ordinately in response to particular metabolic signals. The resultant integrated response to nutrient challenge allows the organism to survive and flourish in a variety of environmental conditions while minimal energy is expended upon the production of unnecessary proteins. The Zn(II)2Cys6 family of transcriptional regulators is composed of some 46 members in S. cerevisiae and many of these have been implicated in mediating transcriptional responses to specific nutrients. Gal4p, the archetypical member of this family, is responsible for the expression of the GAL genes when galactose is utilized as a carbon source. The regulation of Gal4p activity has been studied for many years, but we are still uncovering both nuances and fundamental control mechanisms that impinge on its function. In the present review, we describe the latest developments in the regulation of GAL gene expression and compare the mechanisms employed here with the molecular control of other Zn(II)2Cys6 transcriptional regulators. This reveals a wide array of protein-protein, protein-DNA and protein-nutrient interactions that are employed by this family of regulators.