Electron microscopic studies of guinea pig hepatocyte chromatin.

Chromatin from guinea pig hepatocytes has been studied by electron microscopy using the spreading technique. Among DNP fibers with nucleosomal organization numerous structures with different organization have been observed. The structures consist of the main axial fiber from which the lateral fibrils branch off normal to the axis. The distances between the bases of lateral fibrils vary to a considerable extent. The lateral fibrils are composed of regular granules with an average diameter of 257 A, and the axial fiber of irregularly and rarely arranged granules. The structures described are thought to be nonribosomal transcription complexes, and the granules of lateral fibrils — nuclear informosomes. The longest lateral fibril may have up to 80 granules (informosomes), which corresponds to a pre-mRNA chain of about 15–17×106 daltons.