Recognition of multimolecular G-quadruplex regulates phase separation of cockayne syndrome B

Cockayne syndrome B (CSB) is a multifaceted protein with known functions in DNA repair and transcription elongation. We recently demonstrated that CSB can recognize DNA secondary structures known as multimolecular G4s (mG4s) with high selectivity, but the potential biological significance of this interaction remains to be elucidated. In this study, we report that CSB can undergo liquid-liquid phase separation (LLPS), a process heavily linked with transcriptional regulation. Importantly, we found that the binding of CSB to mG4s promotes LLPS, leading to the physical segregation of DNA sequences containing mG4s within CSB-mG4 droplets from those lacking this structural motif. Furthermore, we revealed that mG4-binding alters the physicochemical properties of the phase-separated CSB, including increased salt resistance and decreased in-droplet mobility. Given the growing evidence supporting an active role for G4s in stimulating transcription, we anticipate that the selective LLPS displayed by CSB upon mG4 binding may be relevant in the context of transcriptional regulation.