Molecular analysis of a genetic switch. (360G-Wellcome-078464_Z_05_Z)

The Saccharomyces cerevisiae GAL genes encode the enzymes of the Leloir pathway. The genes are transcriptionally active when yeast cells are grown in medium containing galactose as the sole source of carbon. Under other carbon source conditions, however, the GAL genes are transcriptionally inert. The switch between inactive and active gene expression is controlled by the interplay of three proteins (the transcriptional activator Gal4p, the transcriptional inhibitor Gal80p and the transcriptional inducer Gal3p) and two small molecules (galactose and ATP). Despite decades of genetic and biochemical analysis, the molecular details by which the switch responds to galactose are poorly understood. Recent advances from my own laboratory have, however, led to extraordinary new insights into the transcriptional control ofthe GAL genes. We have already initiated, and will continue and extend during the course of this award, a structural analysis of the GAL regulatory proteins. In addition, the cellular site of interaction between Gal80p and Gal3p that occurs in the presence of galactose will be determined directly using a combination of biochemical and microscopy analysis. The data generatedduring the course of this award will, finally, determine the precise molecularmechanism of this well-studied genetic switch.