# Transcriptional activation by Rap1p, Gcr1p and Gcr2p in the yeast Saccharomyces cerevisiae

#### Abstract

In the yeast Saccharomyces cerevisiae, efficient expression of most glycolytic genes requires three transcription factors: Rap1p, Gcr1p and Gcr2p. In this study, I have demonstrated a functional relationship among these factors which leads to a model that explains the different requirements in UAS$\sb{\rm rpg}$-dependent (Rap1p-bound) promoters with respect to their requirement for the three factors. Since I was able to co-immunoprecipitate Gcr1p and Rap1p in vitro, we proposed that Gcr1p and Rap1p form a complex in vivo, a working model that is now well supported by other genetic and biochemical evidence. I have demonstrated that Gcr2p's role in the cell is to mediate the CT box effect; I have also shown evidence suggesting that this specialized function of the Rap1p/Gcr1p complex may be regulated by a conformational change in Gcr1p. By further investigation along these lines, I have discovered that Gcr1p is phosphorylated primarily in a region that is dispensable for Gcr1p function. However, mutant alleles with this region deleted can now bypass the requirement for Gcr2p. Furthermore, I present evidence suggesting that phosphorylation of Gcr1p may regulate its stability and that Gcr2p is required for the hyper-phosphorylation of Gcr1p. Further implications of the transcriptional activation by Rap1p/Gcr1p/Gcr2p are discussed.