Sugarcoating Polycomb repression.

The addition of the monosaccharide O-GlcNAc is one of the most mysterious posttranslational modifications. In this issue of Developmental Cell, Gambetta and Müller (2014) show that O-GlcNAcylation of the Drosophila Polycomb group (PcG) protein Polyhomeotic (PH) is essential for homeotic gene silencing. O-GlcNAcylation counteracts nonproductive aggregation of PH, allowing transcriptional repression.