Discovery and Characterization of a Cellular Potent Positive Allosteric Modulator of the Polycomb Repressive Complex 1 Chromodomain, CBX7

Cell Chem Biol. 2019 Oct 17;26(10):1365-1379.e22. doi: 10.1016/j.chembiol.2019.07.013. Epub 2019 Aug 15.


Polycomb-directed repression of gene expression is frequently misregulated in human diseases. A quantitative and target-specific cellular assay was utilized to discover the first potent positive allosteric modulator (PAM) peptidomimetic, UNC4976, of nucleic acid binding by CBX7, a chromodomain methyl-lysine reader of Polycomb repressive complex 1. The PAM activity of UNC4976 resulted in enhanced efficacy across three orthogonal cellular assays by simultaneously antagonizing H3K27me3-specific recruitment of CBX7 to target genes while increasing non-specific binding to DNA and RNA. PAM activity thereby reequilibrates PRC1 away from H3K27me3 target regions. Together, our discovery and characterization of UNC4976 not only revealed the most cellularly potent PRC1-specific chemical probe to date, but also uncovers a potential mechanism of Polycomb regulation with implications for non-histone lysine methylated interaction partners.

Keywords: allosterism; chromatin; chromodomain; methyl-lysine reader; polycomb; positive allosteric modulator.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allosteric Regulation / drug effects
  • Animals
  • Drug Discovery*
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Mice
  • Peptidomimetics / chemistry
  • Peptidomimetics / pharmacology*
  • Polycomb Repressive Complex 1 / metabolism*


  • CBX7 protein, human
  • Peptidomimetics
  • Polycomb Repressive Complex 1