Assessing effect of CEBPA degradation on rRNA transcription machinery

We report the effect of degradation of CEBPA (a critical myeloid lineage transcription factor) on the occupancy of core rRNA transcription machinery on rDNA in mouse GMP cells. We generated a CEBPA-Degron line by tagging endogenous alleles of the Cebpa gene with the FKBPV degron domain, and degraded CEBPA-FKBPV-FLAG fusion protein using dTAGV-1 ligand. We used anti-FLAG pulldown to demonstrate binding of CEBPA protein to rDNA at a conserved motif within the 18S transcribed region. On degradation of CEBPA, we found that RPA194 (component of Pol I) and RRN3 occupancy on rDNA were reduced, while the occupancy of upstream factors TAF1B (component of SL-1) and UBTF were unchanged. In parallel, we also found that CEBPA degradation reduced nascent rRNA transcription, cellular ribosome abundance, and cell growth. Our work indicates that the cell-type-specific transcription factor CEBPA recruits the Pol I-RRN3 complex to ribosomal DNA to promote rRNA transcription. Examination of the effect of CEBPA degradation on rRNA transcription machinery using timecourse ChIP-Seq (2 replicates per timepoint) of RPA194 (component of Pol I), RRN3, TAF1B (component of SL-1), and UBTF.