FIGURE 9-47 Maintenance of histone H3 lysine 9 methylation during chromosome replication. When chromosomal DNA is replicated, the parent histones randomly associate with the two daughter chromosomes, while unmethylated histones synthesized during S phase are assembled into other nucleosomes in those same daughter chromosomes. Association of histone H3 lysine 9 methyl transferases (H3K9 HMT) with parent nucleosomes bearing the histone 3 lysine 9 di- or trimethylation mark methylates the newly added unmodified nucleosomes. Consequently, histone H3 lysine 9 methylation marks are maintained during repeated cell divisions unless they are specifically removed by a histone demethylase.