FIGURE 1: Microscopy-based screen to identify novel ribosome biogenesis inhibitors. ~1000 compounds of commercially available collections (Enzo and NIH) were tested for their ability to inhibit maturation of the large or small ribosomal subunits. Positively scoring compounds were indicated by a shift of the cytoplasmic (untreated) localization of GFP-tagged ribosomal reporter proteins into either the nucleolus or the nucleoplasm. The effects of the identified compounds were further characterized by northern blot analysis to detect specific rRNA processing defects, which gives a first hint at the inhibited maturation stage.