[Ultrastructural demonstration of deoxyribonuclease-sensitive elements in fibrillar zones of the nucleoli of L 929 cell interphasic nuclei].

We have shown in our earlier paper (4) that a ribonuclease resistant filamentous network was associated with the fibrillar structures of the nucleolus of L 929 interphase nucleus. After desoxyribonuclease digestion and oxydised DAB opacification, the nucleolar fibrillar areas became heterogenous from an electron microscopical point of view. We have concluded that an important part of these fibrillar areas are composed of DNA and that the high electron dense fibrillar structures seen after desoxyribonuclease digestion, are the primary ribosomal gene product, just transcribed on the DNA matrix.