Nuclear functions of CFAP20 in transcription and replication [ChIP-seq TY-CFAP20]

Fine-tuning DNA replication and transcription co-occurrence is vital to avoid collisions between their machineries. This is especially relevant near promoters, where RNAPII initiates transcription and often arrests, forming R-loops. Arrested RNAPII poses a roadblock for DNA replication, which evolutionarily initiates near promoters. The mechanisms that salvage arrested RNAPII during elongation to avoid conflicts with incoming replisomes remain unaddressed. In this study, employing genome-wide and proteomic approaches, we identify and characterize CFAP20 as part of a protective pathway that rescues arrested RNAPII in promoter-proximal regions, diverting it from the path of co-directional replisomes. CFAP20-deficient cells accumulate R-loops specifically near promoters, displaying defects in replication origin firing and fork progression. Co-depletion of the Mediator coactivator complex or removal of RNAPII engaged with R-loops rescues these replication phenotypes. Therefore, we propose that CFAP20 salvages arrested RNAPII under conditions of high Mediator-driven transcription to promote RNAPII elongation, thereby preventing collisions with co-directional replisomes. To explore spatial connections between transcription and replication at the genome-wide level, as well as the role of CFAP20 in these processes, we mapped RNA polymerase II (RNAPII) and CFAP20 occupancy using chromatin immunoprecipitation (ChIP)-seq, nascent transcription by bromouridine (BrU)-seq and TTchem-seq, and R-loops by DNA-RNA hybrid immunoprecipitation (DRIP)-seq in RPE1 cells being either wild type (WT), CFAP20-KO, CFAP20-KO rescued with CFAP20-GFP, or CFAP20/CCNC-dKO.