Cells were fixed with 4% paraformaldehyde (PFA) and 0.05% glutaraldehyde in PBS. The cells were harvested, gelatin-embedded, and infiltrated with 2.3 M sucrose according to the method described (81). Ultrathin sections were cut at −110°C with an RMC MTX/CRX cryo-ultramicrotome (Boeckeler Instruments Inc.), transferred to carbon- and pioloform-coated electron microscopy (EM) grids, and blocked with 0.3% BSA, 6 mM glycine, 3% CWFG (cold water fish gelatine) in PBS. The sections were incubated with appropriate dilutions in the same buffer of rabbit polyclonal antibody against NE (Calbiochem) and mouse monoclonal antibody against histone-DNA complex. Secondary antibody incubations were performed with goat anti-rabbit or mouse antibodies coupled to 12- or 6-nm gold particles (Jackson ImmunoResearch). Specimens were then contrasted and embedded with uranyl acetate/methyl cellulose as previously described (82) and analyzed in a Leo 906 transmission electron microscope (Zeiss). Transmission electron microscopy images were captured with a side-mount Morada digital camera (SIS). For quantification, high-resolution overview electron micrographs were acquired. Gold particles were automatically identified with the ImageJ plug-in “Golddigger.” Random regions of interest with a size of 2 μm by 2 μm were placed onto the cytoplasm of the cells, and the number of gold particles was determined (for an example, see fig. S21).

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