Rewriting the past: de novo activity of PRC2 restores global H3K27 methylation patterns

Inheritance of Polycomb repressive complex 2 (PRC2)-mediated gene silencing involves self-propagation of histone H3 lysine 27 (H3K27) methylation from an initial nucleation site, but how the first H3K27 methylation marks are established is not fully understood. A recent study reveals that PRC2 can reconstitute H3K27 methylation de novo in cells that have lost the mark. This reconstitution is dependent on the PRC2 core component SUZ12, which provides a novel link between initiation and self-propagation of this critical epigenetic mark.