LAUSR

Chromosome higher-order structure has been an enigma for over a century. Proposed models include radial loop model, radial coil model, folded fiber model and helical coiling of radial loops model [1]. These models are based on the assumption that DNA is wrapped around histones and forming nucleosomes, and nucleosome fiber with 11nm is folded into a 30nm basic chromatin fiber. The 30 nm chromatin fibers in chromosomes have been observed by SEM, TEM and TEM tomography. Several results also support existence of 30 nm chromatin fiber structure [2, 3]. On the contrary, the 30 nm chromatin structures in mitotic chromosomes were not found by cryo-EM [2, 3] and small-angle X-ray scattering results. Larger 200-400 nm structures consisted of the 30 nm fibers have also been observed although the structures have not been supported by several results.