Summary of Measurements of Electron Micrographs of Chromatin with PSC.

Table indicates mean +/− standard deviation for three measurements from two experiments. Each template uses a plasmid containing two 601 nucleosome positioning sequences that is assembled at low ratios of histones to DNA (0.2 histone:DNA by mass). The first set template has ∼1600 bp between the 601 nucleosomes and the second has 385 bp. Diameter is the maximum diameter of each template (the diameter of the smallest circle that would completely encompass the template) [15]. The maximal diameter of each particle on each template was measured, giving rise to the “particle diameter” measurement. For –PSC samples, particles should be nucleosomes, while in +PSC samples, they could be nucleosomes, PSC bound to naked DNA, or PSC bound nucleosomes. Note that the largest diameter of the disk-shaped nucleosome is 11 nm; samples were rotary shadowed to a thickness of 3.75 nm; thus, the diameter measured is consistent with expectation (11+2×3.75 = 18.5 nm predicted size). The number of particles indicates each separate particle on a template, irrespective of size.