Chromatin remodeling by transcriptional activation domains in a yeast episome

We examine the generality of transcription factor-mediated chromatin remodeling by monitoring changes in chromatin structure in a yeast (Saccharomyces cerevisiae) episome outside of the context of a natural promoter. The episome has a well defined chromatin structure and a binding site for the transcription factor GAL4 but lacks a nearby functional TATA element or transcription start site, so that changes in chromatin structure are unlikely to be caused by transcription. To separate changes caused by binding and by activation domains, we use both GAL4 and a chimeric, hormone-dependent activator consisting of the GAL4 DNA-binding domain, an estrogen receptor (ER) hormone-binding domain, and a VP16 activation domain (Louvion, J.-F., Havaux-Copf, B. and Picard, D. (1993) Gene (Amst.) 131, 129-134). Both GAL4 and GAL4.ER.VP16 show very little perturbation of chromatin structure in their nonactivating configurations. Substantial additional perturbation occurs upon activation. This additional perturbation is marked by changes in micrococcal nuclease cleavage patterns, restriction endonuclease accessibility, and DNA topology and is not seen with the nonactivating derivative GAL4.ER. Remodeling by GAL4.ER.VP16 is detectable within 15 min following hormone addition and is complete within 45 min, suggesting that replication is not required. We conclude that activation domains can exert a major influence on chromatin remodeling by increasing binding affinity and/or by recruitment of other chromatin remodeling activities and that this remodeling can occur outside the context of a bona fide promoter.