GAL4 PROTEIN-BINDING IS REQUIRED BUT NOT SUFFICIENT FOR DEREPRESSION AND INDUCTION OF GAL2 EXPRESSION

The Saccharomyces cerevisiae GAL2 gene upstream activator sequence (UA S) region was examined for protein bound in vivo by chromatin footprin ting at high resolution. Gal4 transcriptional activator protein binds to the two consensus UAS sites whether GAL2 expression is induced, uni nduced, or repressed by growth with different carbon sources. Although wild type strains show loss of the Gal4 protein-specific footprint in repressing media containing glucose, constitutive high level expressi on of Gal4 protein restores the GAL2 UAS footprints without fully dere pressing GAL2 transcription. Thus binding of the Gal4 activator to tar get sites in the DNA is required but not sufficient for GAL2 derepress ion and induction. Gal4-independent protein-DNA complexes were also de tected in the region, including one over the previously noted centrome re-binding protein (CP1) site upstream of the Gal4 complexes.