CBX4, E3 SUMO-protein ligase CBX4, Chromobox protein homolog 4, Polycomb 2 homolog

Chromobox homolog 4 (CBX4 or Pc2) is a member of Drosophila Polycomb group gene family. The polycomb group (PcG) genes are essential for maintenance of appropriate expression patterns of developmental master regulators and thus are essential for proper development. Changes in expression pf PcG proteins have been associated with cancer. CBX4 is a part of the cellular memory system that is responsible for the inheritance of gene activity by progeny cells. CBX4 is involved in maintaining the transcriptionally repressive state of genes. It modifies chromatin, rendering it heritably changed in its expressibility. Structurally, CBX4 contains 1 chromo domain. It was reported that Pc2 is involved in sumoylation process by recruiting SUMO E1 and E2, and Pc2 is actually SUMO E3 during sumoylation events. CBX4 expression is ubiquitous.