The function of heterochromatin has not been well understood. Recent studies, however, demonstrate that heterochromatin is essential for proper chromosome behavior. The silencing of euchromatic genes by heterochromatin has been exploited to understand the molecular nature of heterochromatin. Mutations that either suppress or enhance gene silencing exist within chromatin structural proteins and modifying enzymes. Interactions between some of these proteins have been demonstrated, suggesting a complicated picture of heterogeneous silencing complexes that are counteracted by protein-modifying machinery.