TY - JOUR T1 - Natural chromatin is heterogeneous and self associates <em>in vitro</em> JF - bioRxiv DO - 10.1101/139543 SP - 139543 AU - Shujun Cai AU - Yajiao Song AU - Chen Chen AU - Jian Shi AU - Lu Gan Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/05/18/139543.abstract N2 - The 30-nm fiber is commonly found in oligonucleosome arrays in vitro but rarely found in chromatin within nuclei. To determine how chromatin high-order structure is controlled, we used cryo-ET to study the undigested natural chromatin released from cells that do not have evidence of 30-nm fibers in vivo: picoplankton and yeast. In the presence of divalent cations, most of the chromatin from both organisms is compacted into a large mass. Rare irregular 30-nm fibers do form at the periphery of this mass, some of which include face-to-face interactions. In the absence of divalent cations, picoplankton chromatin decondenses into open zigzags. By contrast, yeast chromatin mostly remains compact with looser nucleosome packing, even after treatment with histone-deacetylase inhibitor. The 3-D configuration of natural chromatin is therefore sensitive to the local environment, but generally nonpermissive of regular motifs, even at the level of oligonucleosomes. ER -