CBP regulates promoter-proximal RNA polymerase II

Transcription activation involves RNA polymerase II (Pol II) recruitment and release from the promoter into productive elongation, but how specific chromatin regulators control these steps is not fully understood. Here we identify a novel activity of the co-regulator and histone acetyltransferase p300/CBP in positioning promoter-proximal paused Pol II. We find that CBP inhibition impedes transcription through the +1 nucleosome, causing “dribbling” of Pol II from the canonical pause site genome-wide. We further discovered that promoters strongly occupied by Drosophila CBP and GAGA-factor have high levels of paused Pol II, a unique chromatin signature and strong expression regardless of cell type. Interestingly, CBP activity is rate-limiting for Pol II recruitment to these highly-paused promoters but for transit into elongation at other genes. Thus, we uncover a key role for CBP during transcription in directly controlling different rate-limiting steps depending on promoter features. Overall design: Examination of transcriptional regulation with and without CBP inhibition for 10 minutes in Drosophila S2 cells. Two biological replicates for each condition.