TEM images of reconstituted chromatin prepared from 12-mer tandem repeats of a strong nuclear positioning sequence and purified histones. Samples were compacted in the appropriate salt, and mildly crosslinked with formaldehyde to preserve nucleosome-nucleosome interactions, then allowed to decondense in low salt prior to fixation with glutaraldehyde, and shadowing with Pt. (B-D with linker histone and without Mg; J-M) with linker histone and 1 mM MgCl2; (N-S)with linker histone and 4mM MgCl2. The drawings at right show the authors' interpretation of the adjacent micrograph showing crosslinked nucleosomes and the number of nucleosomes included in the 'loop' created by the crosslink. See Fig 3 in S A Grigoryev et al. 2009 Evidence for heteromorphic chromatin fibers from analysis of nucleosome interactions. Proc Natl Acad Sci USA 106:13317-13322 See Fig 1 in: S A Grigoryev et al. 2009 Evidence for heteromorphic chromatin fibers from analysis of nucleosome interactions. Proc Natl Acad Sci USA 106:13317-13322