Acetylation-dependent clustering of BRD2 instructs transcription dynamics

BET protein inhibitors represent one of the most prominent classes of epigenetic drugs. However, the specific contributions of individual BET family members to transcription regulation remain largely unknown. Here, by acutely co-depleting BET proteins, we uncover an essential role of BRD2 in maintaining RNA Polymerase II recruitment at promoters, which becomes especially critical in the absence of BRD4 or when pause release is inhibited. Combining rapid protein degradation, chemogenomics, and super-resolution microscopy, we show that H4 acetylation, particularly H4K16ac, serves as a template for BRD2 function, driving sub-diffraction BRD2 cluster formation at chromatin. Accordingly, depletion of BRD2 or the writer of H4K16ac, MOF decreases sub-diffraction RNA Polymerase II clusters, which are associated with transcription initiation. Thus, this study highlights the importance of acetylated chromatin in transcriptional coactivator organization and the distinct role of BRD2 in transcription initiation dynamics.