CBP-IDRs regulate acetylation and gene expression.

Intrinsically disordered regions (IDRs) are essential regulators of protein function despite lacking stable secondary and tertiary structures. IDRs are integral to the function of multidomain regulatory proteins, such as the essential transcriptional coactivators cAMP response element-binding protein (CREB)-binding protein (CBP) and EP300 (p300), but how their multiple IDRs work together to regulate function remains poorly understood. Here, we demonstrate that different CBP-IDRs cooperate to control complex nuclear behaviors. We show how CBP-IDRs with different sequence properties make unique contributions to CBP behavior, establishing a critical balance between positive and negative regulation of CBP condensates. These opposing interactions are functionally important, tuning CBP's sensitivity to regulatory cues such as lysine acetylation. Disruption of this balance fundamentally alters CBP's chromatin occupancy, patterns of histone acetylation, and downstream gene expression. Together, our work reveals an unexpected mechanism of intramolecular cooperation between distinct IDRs and highlights how their properties shape the functional landscape of multi-domain proteins.