Ultrastructural organization and biochemical characterization of chromatin - RNA - protein complexes isolated from mammalian cell nuclei.

Extranucleolar elements were isolated from mammalian cell nuclei and characterized by correlative biochemical-ultrastructural studies. These complex structures were shown to retain a supra-particle arrangement closely resembling the organization in situ of definite nuclear areas. In particular the morphological RNA - protein species, namely perichromatin fibrils and granules, were detected in association with characteristic regions of chromatin. By autoradiographic experiments, we were able to show that perichromatin fibrils represent the morphological state of newly formed heterogeneous nuclear RNA (hnRNA). Chromatin - RNA - protein complexes were further fractionated by means of a treatment dissociating the chromatin component. A minor part of DNA, possibly involved in the biosynthesis and the processing of hnRNA, remains linked to the resulting RNA - protein network.