The induction of nucleolar fragmentation and the inhibition of RNA synthesis in HeLa cells by MPB and their restoration

The effects of MPB on the staining intensity of pyronine G, the fine structure of HeLa cell nucleoli and RNA synthesis were investigated. MPB (50 μg/ml) produced a loss of pyronine G staining material (RNA) and fragmentation of nucleoli in HeLa cells within 3 h; however, these changes in nucleoli were rapidly reversed by removal of the drug. These morphological alterations of nucleoli were apparently related to the inhibitory action of MPB on nucleolar RNA synthesis in HeLa cells, and its reversibility.