Abstract
Sometimes it is necessary to silence genes, a process that involves shutting down regions of active chromatin. Genes can be silenced by methylation of lysine 9 in histone H3 of chromatin, but RNAi also turns out to be important in chromatin-based gene silencing. In a Perspective, Robin Allshire discusses new work (Volpe et al.) that shows how RNAi is able to shut down chromatin in fission yeast by promoting H3 lysine 9 methylation, perhaps by altering the recruitment of enzymes that methylate DNA and histones.