EM images of chromatin fibers reconstituted from tandem arrays of a strong nucleosome positioning sequence flanked by different lengths of 'linker' DNA, to create nucleosome repeat lengths (NRL) from 177 bp to 237 bp. Reconstitutes had saturating amounts of purified core histones and linker histones. (A) shows the range of structures seen with glutaraldehyde fixation and negative staining, with the left panel illustrating individual fibers and the right panel longer structures consisting of end-to-end aggregates.(B)shows images of a single NRL after cryo-fixation and recorded in the frozen hydrated state. See Fig 1 in P.J. Robinson et al. 2006. EM measurements define the dimensions of the "30-nm" chromatin fiber: Evidence for a compact, interdigitated structure. Proc Natl Acad Sci USA 103:6506-6511.