Figure 1. H2B ubiquitylation impairs fiber folding.

a, Ubiquitylated H2B appears incompatible with nucleosome stacking. Upper panel: Model of a 30 nm chromatin fiber (1ZBB, ref. 9). Lower panel: The structure of a tetranucleosome unit extracted from the fiber and rotated by 38.1° ⁹. The sites of ubiquitin attachment are shown in red, whereas the fluorescein labeling site is shown in green. b, Sedimentation coefficient distributions for unmodified and uH2B_SS containing chromatin arrays (black and red symbols) are determined by sedimentation velocity experiments and van Holde-Weischet analysis at 0 and 1 mM Mg²⁺ (solid and open symbols). Inset: ubiquitin is attached via disulfide based coupling chemistry ²⁶. c, S_20,w values of unmodified (black) and uH2B_SS containing arrays (red) are shown as a function of Mg²⁺ concentration. Error bars, standard deviation (n=3).