The 30 nm filament, a higher-order organization of nucleosomes. The compact filament is formed by the tight packing of nucleosomes. (a) The 30 nm filament as seen by electron microscopy. Two proposed models of filament structure are (b) the solenoid model and (c) the zigzag model. The path of DNA is shown as a dark brown line through the histones, for clarity of histone visualization.