Regulator of histone methyltransferase complexes that plays an essential role in embryonic development. Acts by modulating histone methyltransferase activity and promoting the recruitment of histone methyltransferase complexes to their target genes. Binds DNA and mediates the recruitment of the PRC2 complex to target genes in embryonic stem cells. Does not have histone demethylase activity but regulates activity of various histone methyltransferase complexes. In embryonic stem cells, it associates with the PRC2 complex and inhibits trimethylation of 'Lys-27' of histone H3 (H3K27me3) by the PRC2 complex, thereby playing a key role in differentiation of embryonic stem cells and normal development (By similarity). Associates with the PRC2 complex. Colocalizes with the PRC2 complex on chromatin. The ARID domain is required to target the PRC2 complex to its target genes. Belongs to the JARID2 family.