Unwrapping DNA from nucleosomes
At the lowest level, compaction is achieved by wrapping stretches of DNA around a core of histone proteins to form nucleosomes in a “beads on a string” configuration: 147 base pairs of DNA per nucleosome, with linkers of variable length between nucleosomes. The nucleosome core particle (NCP), or one “bead”, consists of 4 types of histone (H2A, H2B, H3, and H4), each of which has a compact core plus a positively-charged, flexible tail that protrudes from the core.