In nature, individual histones in the same nucleosome can carry identical (symmetric) or different (asymmetric) post-translational modification (PTM) patterns, increasing the combinatorial complexity. Embryonic stem cells exhibit bivalent nucleosomes, some of which are marked by an asymmetric arrangement of H3K36me3 (an activating PTM) and H3K27me3 (a repressive PTM). Here we describe a modular synthetic method to access such asymmetrically modified nucleosomes and show that H3K36me3 inhibits the activity of the methyltransferase PRC2 locally while still prolonging its chromatin binding time.