Fig. 4

Inhibitors induce different rRNA processing defects. a Schematic picture of the longest rRNA precursor (35S pre-rRNA) containing the sequences of the mature 18S rRNA, the 5.8S rRNA and the 25S rRNA, which are interrupted and flanked by internal (ITS) and external (ETS) transcribed spacers, respectively. The region encompassing ITS1 and ITS2 is enlarged and the main processing sites (A₂, A₃, B₁, C₁, C₂, D, and E) are indicated. Hybridization sites of probes used in the northern blotting experiment are indicated by green bars. The entire processing pathway is displayed in Additional file 1: Figure S1. b, c Examples of northern blots after treatment with substances found in the 40S reporter screen (b, blue lettering), in the 60S reporter screen (c, red lettering) or in both screens (c, grey lettering). The detected rRNA species are indicated on the right side, the probes used to detect the respective pre-rRNAs are indicated on the left side. The northern blots for all 128 compounds are shown in Additional file 1: Figures S10 and S11. d Hierarchical clustering of the indicated pre-rRNA/rRNA ratios. The color code in the heatmap indicates increased (purple) or decreased (yellow) levels of the respective precursors normalized to the mock control (DMSO) and then referenced to the respective mature rRNA in the same sample. Inhibitors found in the 60S reporter screen are marked by red lettering, inhibitors from the 40S screen are written in blue and inhibitors identified in both screens in grey. The control diazaborine was included once with the same DMSO concentration used in the screen with the NIH substances and once with the DMSO concentration used in the Enzo screen. Both conditions were found in the same cluster, demonstrating neglectable effects of the different DMSO concentrations