Molecular model of a human H2AK119Ub nucleosome complexed with DNA (deoxyribonucleic acid) methyltransferase 3A (DNMT3A, yellow-green). H2AK119 refers to a specific histone protein (H2A, red), and the number 119 indicates the 119th amino acid position in this protein chain. Bu refers to the attachment of ubiquitin (purple) to the H2A histone protein at the 119th amino acid position. Histone H3.3C is shown in cyan, H4 in grey, histone H2B1.1 in blue.