Fig. 1. Influence of irofulven on RNA synthesis. (A) HeLa cells were incubated with the indicated concentrations of irofulven for 1 hour and the influence on RNA synthesis was measured by incorporation of radiolabeled uridine. Error bars represent standard errors. (B) HeLa cells were exposed for 1 hour to actinomycin D, DRB or irofulven at the indicated concentrations, permeabilized and the engaged polymerases allowed to extend their transcripts in the presence of bromo-UTP. Nascent RNAs were revealed by immunolabeling of bromo-labeled nucleotides. (C) HeLa cells were exposed for 1 hour to irofulven at the indicated concentrations. 15 minutes before fixation, bromo-uridine was added to the medium. Bromo-labeled RNAs were revealed by immunolabeling.