Overview of chromatin organization. Inside the nucleus of a cell, chromosomes exist in discrete chromosomal territories. The chromatin that makes up the chromosomes is packaged differently at different loci. Regions of euchromatin within these territories tend to cluster in the center of the nucleus, whereas regions of heterochromatin tend to associate with the periphery. In euchromatin, nucleosomes are less tightly packed and display histone modifications associated with transcriptional activation. In heterochromatin, the nucleosomes are tightly packed and have histone modifications associated with repression. Both active and repressive histone modifications are regulated by writer, reader and eraser proteins. Illustrated beneath the image is a summary of the currently used clinical compounds in AML that target epigenetic writers, readers, and erasers. BRD, bromodomain-containing protein; Cbx2, chromobox 2; DNMT, DNA methyltransferase; DOT1L, disruptor of telomeric silencing 1-like; Ezh2, enhancer of zeste homolog 2; HDAC, histone deacetylase; Kdm6A, lysine demethylase 6A; LSD1, lysine-specific histone demethylase 1; PRMT5, protein arginine N-methyltransferase 5.