Co-condensation between transcription factor and coactivator p300 modulates transcriptional bursting kinetics

The coactivator p300/CBP regulates genes by facilitating the assembly of transcriptional machinery and by acetylating histones and other factors. However, it remains mostly unclear how both functions of p300 are dynamically coordinated during gene control. Here, we showed that p300 appears to orchestrate two functions through the formation of dynamic co-condensates with certain transcription factors (TFs), which is mediated by the interactions between the TF's trans-activation domain (TAD) and the intrinsically disordered regions (IDRs) of p300. Co-condensation enables spatially defined, all-or-none activation of p300's catalytic activity, priming the recruitment of other coactivators including Brd4. We further revealed that co-condensation modulates transcriptional initiation rate and burst duration of target genes, underlying nonlinear and cooperative gene regulatory functions. Intriguingly, such modulation is consistent with how p300 shapes transcriptional bursting kinetics globally. Together, complementary lines of evidence suggest a new p300-mediated gene control mechanism, where TF and p300 co-condensation contributes to transcriptional bursting regulation and cooperative gene control. Overall design: Examination of RNA expression levels in mouse embryonic stem cells (mESC) WT cell line and in a p300 knock-in mESC cell line. The knock-in cell line (i.e., MLC460) was created by fusing monomeric enhanced green fluorescent protein (mEGFP) to the N-terminus of the endogenous p300 (mEGFP-p300) using CRISPR/Cas9. Two biological replicates were made for each cell line.