Chromobox Homolog 4 (CBX4)

'Polycomb' (Pc) and other members of the Drosophila Polycomb group gene family are part of a cellular memory system that is responsible for the inheritance of gene activity by progeny cells. Pc shares a homologous domain known as the chromodomain with the Drosophila heterochromatin-binding protein, HP1. To isolate human Pc homologs, Satijn et al. (1997) screened a fetal brain cDNA library with a probe containing the nonchromodomain portion of a Xenopus Pc homolog (XPc). They recovered a cDNA encoding a predicted 558-amino acid protein that they designated human Pc2. Human Pc2 and XPc share 48% protein sequence identity. Northern blot analysis revealed that human Pc2 is expressed as a 2.8-kb transcript in all tissues tested with almost equal abundance.