The heterochromatin protein 1 (HP1) family, which consists of isoforms HP1- (CBX5), HP1- (CBX1), and HP1- (CBX3), are chromatin-associated proteins involved in gene regulation and heterochromatin formation.1 CBX proteins have an N-terminal chromodomain, a C-terminal chromoshadow domain, and a hinge domain that connects the two.2 Extensive post-translational modifications have been observed and mapped on the CBX proteins.3 The chromodomain of CBX3 has been shown to recognize methylated histone H3 lysine 9, methylated histone H1 lysine 26, and G9A methylated at lysine 185.4 CBX3 associates with the exons of a subset of actively transcribed genes, and loss of CBX3 results in accumulation of unspliced mRNA from that subset of genes.5,6 Further, CBX3 suppresses Nanog gene transcription in pre-induced pluripotent stem cells and long terminal repEAt protein expression in HIV-1 infected cells.6,7 Knockdown of CBX3 by siRNA in cells latently infected with HIV-1 lEAds to virus rEActivation.8 CBX3 has been proposed to be a biomarker for tumor stem cells in osteosarcoma.9 Technical Information Synonyms Chromobox Protein Homolog 3 Heterochromatin Protein 1 Homolog HP1- Purity 95% (estimated by SDS-PAGE) Source Recombinant N-terminal GST-tagged protein expressed in E. coli MW 48.4 kDa Formulation 50 mM Tris, pH 7.4, containing 150 mM sodium chloride and 20% glycerol UniProt Accession Q13185