Fig. 3. Nuclear accumulation of rRNAs upon leptomycin B (LMB) treatment of HeLa cells. Localization of rRNAs was analyzed in untreated HeLa cells or cells that had been treated with LMB for 18 hours by fluorescent in situ hybridization (FISH) using digoxigenin-labeled oligonucleotides directed to 18S and 28S rRNA, respectively. To control for the specificity of the detection, cells were either treated with RNaseA before FISH analysis or the probes were omitted (upper panels). Images were taken by confocal fluorescence microscopy.