Histone H1 of Saccharomyces cerevisiae inhibits transcriptional silencing

Eukaryotic genomes contain euchromatic regions, which are transcriptionally active, and heterochromatic regions, which are repressed. These domains are separated by "barrier elements": DNA sequences that protect euchromatic regions from encroachment by neighboring heterochromatin. To identify proteins that play a role in the function of barrier elements we have carried out a screen in S. cerevisiae. We recovered the gene HHO1, which encodes the yeast ortholog of histone H1, as a high-copy modifier of barrier activity. Histone H1 is a linker histone that binds the outside of nucleosomes and modifies chromatin dynamics. Here we show that Hho1p reinforces the action of several types of barrier elements, and also inhibits silencing on its own.