THE YEAST COACTIVATOR GAL11 POSITIVELY INFLUENCES TRANSCRIPTION OF THE PHOSPHOGLYCERATE KINASE GENE, BUT ONLY WHEN RAP1 IS BOUND TO ITS UPSTREAM ACTIVATION SEQUENCE

Transcription of the yeast phosphoglycerate kinase gene (PGK) is activ ated by an array of nuclear factors including the multifunctional prot ein RAP1. We have demonstrated that the transcriptional co-activator G AL11, which was identified as an auxiliary factor to GAL4 and which is believed to interact with the zinc finger of the trans-activator, pos itively influences the level of PGK transcription on both fermentable and non-fermentable carbon sources. This positive effect is only obser ved when the RAP1. site in the upstream activation sequence (UAS) is p resent, implying that GAL11 acts through RAP1. Expression of the RAP1 gene is not reduced in the gal11 background, and in vivo footprinting shows that GAL11 does not influence RAP1 DNA-binding activity. Therefo re the effect of GAL11 on PGK transcription must be mediated at the PG K UAS, presumably as part of the activation complex. It has been propo sed that RAP1 may act as a facilitator of GCR1 binding at the PGK UAS and therefore it is conceivable that the target for GAL11 may in fact be GCR1. A further implication of this study is that GAL11 can interac t with proteins such as RAP1 or GCR1 that are apparently structurally dissimilar from GAL4 and other zinc finger DNA-binding proteins.