Figure 1.
Self-assembly of metaphase chromatin fragments into multilayered plates. (A) Transmission electron microscopy (TEM) images of native metaphase chromosomes. (B) TEM images of chromatin fragments from nuclease-digested chromosomes; the sample was diluted 10- to 20-fold with a low ionic strength buffer (1 mM PIPES, pH 7.2, and 1 mM EDTA) before spreading. (C and D) Examples of TEM images corresponding to planar structures formed by association of metaphase chromatin fragments dialyzed at 4°C against the self-assembly solution (10 mM PIPES, pH 7.2, 120 mM KCl, 20 mM NaCl, and 17 mM MgCl2) before spreading. (Head arrows in C) 30-nm circular structures corresponding to chromatin fragments folded as short interdigitated solenoids (26,28,29) oriented with their axes perpendicular to carbon and plate surfaces. Scale bars: 500 nm (A); 100 nm (B); 200 nm (C and D).