Persistence of increased levels of ribosomal gene activity in CHO-K1 cells treated in vitro with demethylating agents.

The rate of ribosomal gene activity was evaluated by silver staining of the Nucleolus Organisers (NOs) in cultured CHO-K1 cells after a 12 h pulse with two demethylating agents (L-ethionine and 5-azacytidine). Silver staining of the NOs was measured every 24 h, from 24 up to 110 h after seeding. The purpose was to test the hypothesis that drug-induced demethylation is associated to heritable modifications of rDNA activity.