Relationship between chromatin and perichromatin granules in cadmium-treated isolated hepatocytes

Abstract

The relationship of perichromatin granules (PG) to transcribing DNA fibrils and nascent hnRNA perichromatin fibrils (PF) was studied in isolated rat liver cells treated with cadmium chloride (CdCl 2 ) in order to increase the number of PG. Demonstration of their in situ organization was made possible by submitting the CdCl 2 -treated cells to a procedure which induced a partial decondensation of nuclear components. These decondensed preparations were combined with cytochemical stains for DNA and RNP, enzymic digestions with DNase and RNase, and autoradiography after pulse labeling with [5- 3 H]uridine, and the results were compared with Miller spreads of completely decondensed chromatin. We found that many if not all PG were attached to DNA fibers by short RNP fibrils. On the basis of their labeling with 5-min pulses of [5- 3 H]uridine and the reported effect of CdCl 2 to block the processing but not the synthesis of hnRNA, we propose that the PG induced by CdCl 2 develop during the course of transcription by the coiling of nascent RNP fibrils.