Scaffold protein that serves as a bridging partner between the PRC2/EZH2 complex and the elongin BC complex: required to fine-tune the transcriptional status of Polycomb group (PcG) target genes in embryonic stem cells (ESCs). Plays a key role in genomic regions that display both active and repressive chromatin properties in pluripotent stem cells by sustaining low level expression at PcG target genes: acts by recruiting the elongin BC complex, thereby restricting excessive activity of the PRC2/EZH2 complex. Interaction with USP7 promotes deubiquitination of H2B at promoter sites. Acts as a regulator of neuronal differentiation. Associates with the PRC2 complex, which consists of the core components EED, EZH1 or EZH2, SUZ12, and RBBP4, and various combinations of accessory subunits including AEBP2, JARID2, PHF19, MTF2 and EPOP (PubMed:24550272, PubMed:29499137). Within the complex, interacts with SUZ12 (via C2H2 zinc finger domain); competes with JARID2 for SUZ12 binding (PubMed:29499137). Associates with the elongin BC complex (By similarity). Interacts with USP7 (By similarity). Localizes at both PRC2/EZH2 sites (H3K27me3) and broad H3K4me3 sites on chromatin of embryonic stem cells (ESCs). The BC-box, which mediates binding to the elongin BC complex.