RRN3 and medulloblastoma: Upon binding to the initiation factor factor-IA (TIF-IA, also named RRN3), RNA Pol I is activated and recruited to the ribosomal DNA promoter.44 In medulloblastoma cells with high Myc expression, the increased rRNA synthesis is associated with increased expression of RNA Pol I-specific transcription initiation factor RRN3/TIF-IA.45 Interestingly, repression of rDNA transcription by CX-5461 is irreversible, and the RNA Pol I-RRN3 complex remains irreversibly locked in the pre-initiation complex even after drug removal.