Chromatin fiber loops protruded artificially from nuclei of rat ascites hepatoma cells.

To determine the size and location of supranucleosomal fibers, the isolated and swollen nuclei from rat ascites hepatoma cells were broken mechanically by a homogenizer, and the broken nuclei were observed with an electron microscope, with and without treatment with detergent Joy. The observation of the broken nuclei treated with 0.06% Joy demonstrated that most, but not all the protruded chromatin, had a loop structure. Protrusion of chromatin from nuclear fragments was estimated to be about 0.77 microns in length. The conformation of protruded chromatin mainly consisted of supranucleosomal fiber, and a little of nucleosomal fiber. Electron microscopy also indicated that an anchorage of chromatin was nuclear lamina. Therefore, chromatin loop size of supranucleosomal fiber (solenoid) was about 1.54 microns in length, corresponding to nucleosomal fiber of about 9.24 microns in length.