The chromatin structure of the GAL1 promoter forms independently of Reb1p in Saccharomyces cerevisiae

Positive and negative regulation of the GAL1 promoter of the yeast Saccharomyces cerevisiae results from a network of interactions between transcription factors and chromatin. In this study we used footprinting procedures to characterize these interactions in vivo. DNase I analysis of the GAL1 upstream activating sequence (UAS(GAL1/10)) showed expected Ga14 activator protein binding during growth in galactose, and also revealed binding of the Reb1 protein (Reb1p) during growth in glucose. In addition, we mapped to nucleotide resolution a positioned nucleosome that, in the inactive promoter, packages DNA between the UAS(GAL1/10) and the GAL1 TATA sequence, leaving both of these elements nucleosome free. The nucleosome footprint was lost when the promoter was activated. Surprisingly, mutation of the Reb1p binding site had no effect on nucleosome positioning or on the kinetics or extent of activation or repression of either the GAL1 or GAL10 promoters under any of the conditions assayed.