Fig. 3

Nucleolus, rRNA synthesis and protein biosynthesis. A Morphology of nucleoli after transfection with MA4 and MAF4m. The morphology and number of nucleoli is grossly changed in the presence of both fusion proteins, MA4 and MA4m, respectively. B Design of the RNA Pol I Luciferase reporter gene. A single rRNA promoter has been used to set up a RNA Pol I dependent Luciferase reporter system that is responsive to Actinomycin D. C Reporter gene assays to monitor the activity of a single rRNA promoter in the presence of all tested fusion proteins or their combinations. The TAFIC::GFP fusion was able to enhance the rRNA promoter activity of the reporter gene. All fusion proteins caused a reduction of reporter gene activity. D QRT-PCR experiments of the total production of 45S precursors rRNA. Apart from A4M-single transfected cells, all other cell lines displayed an increasing amount of the 45S precursor RNA. The amount of UBF protein was quantified and remained stable in all tested cell lines. E Protein biosynthesis measured by the Click iT protein synthesis assay. Apart from A4M-single transfected cells, all other cell lines displayed a decreased protein biosynthesis rate. The reduced protein synthesis level could be rescued by the overexpression of TAF1C. F Investigating the nucleolar stress pathway. Either ActD or the presence of t(4;11) fusion proteins caused the steady-state upregulation of p53 and ß-Catenin. A downstream target of the WNT/ß-Catenin signaling pathway, HOXB4, was significantly upregulated by all tested fusion proteins