Nucleosome core displacement in vitro via a metastable transcription factor-nucleosome complex

In order to function, transcription factors must compete for DNA binding with structural components of chromatin, including nucleosomes. Mechanisms that could be used in this competition have been characterized with the use of the DNA binding domain of the yeast GAL4 protein. The binding of GAL4 to a nucleosome core resulted in a ternary complex containing GAL4, the core histone proteins, and DNA. This ternary complex was unstable; upon the addition of nonspecific competitor DNA, it dissociated into either the original nucleosome core particle or GAL4 bound to naked DNA. Nucleosome core destabilization by GAL4 did not require a transcriptional activation domain. These data demonstrate the displacement of nucleosome cores as a direct result of binding by a regulatory factor. Similar mechanisms might affect the establishment of factor occupancy of promoters and enhancers in vivo.