In the upper panel, transmission electron microscopy reveals a tangled mass of ~30nm diameter nuclear chromatin fibers when the contents of the nucleus from erythrocytes of the newt Notophthalmus viridescens were spread on a water surface, fixed with formaldehyde, critical point dried, and metal shadowed. The lower panel shows chromatin from the nucleated erythrocyte of the chicken dispersed in low ionic strength, high pH buffer, centrifuged through a sucrose-formaldehyde cushion onto a carbon film and stained with uranyl acetate. When fully dispersed, the 'beads-on-a-string nucleosomal organization of chromatin is clearly evident.
Figures 121 (upper panel, provided by Hans Ris) and 122 (lower, provided by Ada Olons) from Chapter 4 (Nucleus) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the chapter is available on the ASCB's BioEDUCATE website.
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