The role of nuclei and nucleoli in the control of cell proliferation.

A number of changes have been reported to occur in chromatin of quiescent cells stimulated to proliferate. These changes, indicative of increased transcriptional activity, occur in the early prereplicative phase, several hours before the onset of DNA replication, and are detectable not only in chromatin, but also in isolated nuclei and in whole cells. Most of the increased transcriptional activity can be attributed to an increased activity of the nucleolus; however, extranucleolar genes are also important in the regulation of the cell cycle flow, from G0 to S.