Single-molecule analysis reveals that IPMK enhances the DNA-binding activity of the transcription factor SRF.

Serum response factor (SRF) is a master transcription factor that regulates immediate early genes and cytoskeletal remodeling genes. Despite its importance, the mechanisms through which SRF stably associates with its cognate promoter remain unknown. Our biochemical and protein-induced fluorescence enhancement analyses showed that the binding of SRF to serum response element was significantly increased by inositol polyphosphate multikinase (IPMK), an SRF cofactor. Moreover, real-time tracking of SRF loci in live cell nuclei demonstrated that the chromatin residence time of SRF was reduced by IPMK depletion in fibroblasts. Conversely, elevated IPMK levels extended the SRF-chromatin association. We identified that IPMK binds to the intrinsically disordered region of SRF, which is required for the IPMK-induced stable interaction of SRF with DNA. IPMK-mediated conformational changes in SRF were observed by single-molecule fluorescence resonance energy transfer assays. Therefore, our findings demonstrate that IPMK is a critical factor for promoting high-affinity SRF-chromatin association and provide insights into the mechanisms of SRF-dependent transcription control via chaperone-like activity.