[Electron microscopic examination of hepatocyte nuclei within first hours after partial hepatectomy. III. Changes of DNP fiber diameters of condensed chromatin].

The DNP fibers have been measured on electron microscope photographs of sections of guinea-pig hepatocytes. The condensed chromatin was found to have fibers from 4 to 27 nm in diameter. Within the first hours after partial hepatectomy the distribution of fibers by their diameters is changed. This is correlated with the ethidium bromide binding to chromatin DNP, which reflects the level of the chromatin template activity. Maximal binding to ethidium bromide was observed at 2.5 hours after the operation and the distribution of fiber diameters was shifted towards a smaller diameter, simultaneously, the amount of thinner fibers from 4 to 14 nm in diameter is larger. Five hours after the operation the content of thicker fibers from 14 to 24 nm is reduced, and the intensity of the ethidium bromide binding is decreased. Nine hours later, the ethidium bromide binding was intensified, and the distribution of fiber diameters again shifted to a smaller width. Our data prove that the thickness of DNP fibers of condensed chromatin, which has been thought inactive, depends on the intensity of the template synthesis.