Electron-microscopic visualization of transcriptionally active and less active chromatin fractions from the rat...

The content of histones in transcriptionally active (euchromatin-like (E)) and transcriptionally less active (heterochromatin-like (H)) fractions from the rat ventral prostate was determined. The absolute amount of total histone was less in the E fraction, which contained relatively more stained histone F2b and F3 and less histone F1 than either the H fraction or unfractionated chromatin. The phosphotungstic-acid-stained E fraction was composed predominantly of shorter (50-500 nm) and thinner (5-15 nm) structures. In some preparations, pieces estimated to be 500-1000 + nm in length were present. Spherical structures, from 10 to 20 nm in diameter, some of which were present as 'dimers,' trimers,' or higher-ordered ensembles were seen in the shadow-case E fraction. The stained or shadow-cast H fraction contained longer (200-2000 + nm) and thicker (congruent to 20 nm) fragments with a more complex substructure. When the shadow-cast H fraction was sufficiently dispersed, it had a nodular or 'beaded' appearance.