Abstract
Suv39h1 and Suv39h2 are core components of mouse heterochromatin, where they direct H3K9me3, which is recognized by HP1. In mouse embryonic fibroblasts, heterochromatin retention modes of Suv39h enzymes differ from HP1 and are not sensitive to compounds that impair liquid-liquid phase separation. Suv39h2 contains an N-terminal basic domain that is also present in around 23% of annotated Suv39h orthologs. The Suv39h2 basic domain provides resistance to chromatin-destabilizing agents, such as mitoxantrone and curaxin, and protects H3K9me3 heterochromatin from unfolding or chemically induced histone eviction. This protective function of the basic domain can be transferred to Suv39h1 as an N-terminal fusion. Together, these findings identify the Suv39h2 basic domain as a structural component of heterochromatin and suggest that basic domain extensions help to buffer heterochromatin destabilization.