Interestingly, in agreement with PRC1 purifications from cancer cell lines (Gao et al., 2012), the PCGF1-containing complex associates with RYBP or YAF2 but fails to integrate chromobox domain-containing (CBX) proteins that recognize H3K27me3 (Cao et al., 2002; Wang et al., 2004a). This evidence concerns the gene RYBP and cancer.