The restless epigenome. Most histones form nucleosomes (octameric DNA compaction units). An array of transcription factors share DNA-binding sites in forming complexes with the chromatin modifying enzymes. These enzymes catalyze the give and take of low MW adducts (methyl, acetyl, phosphate groups). Some eukaryotic chromatins conserved motifs of archaeal and bacterial precursors of eukaryotic cells; even the phage of the mitochondrial 5α-proteobacterium might have contributed the gene for the HEH fold domain (helix-extended-region-helix) to its eukaryotic fusion partner.