Tilt series were recorded using the dose-symmetric recording scheme of Serial EM software at a nominal magnification of 64000 and a target defocus of -3.5 ˚ µm. The total dose was set to 91.5 e−/ A˚ A marker-less tilt series alignment was done in IMOD. Nucleosomes were manually picked in IMOD, and 64x64x64 voxel subtomograms (voxel size of 4.4 A) were extracted from the volumes.