Cockayne syndrome protein B (CSB) belongs to the SWI2/SNF2
ATP-dependent
chromatin remodeler family, and CSB is the only
ATP-dependent
chromatin remodeler essential for transcription-coupled
nucleotide excision DNA repair. CSB alone remodels
nucleosomes ∼10-fold slower than the ACF remodeling complex. Strikingly, NAP1-like
histone chaperones interact with CSB and greatly enhance CSB-mediated chromatin remodeling. While chromatin remodeling by CSB and NAP1-like
proteins is crucial for efficient transcription-coupled DNA repair, the mechanism by which NAP1-like
proteins enhance chromatin remodeling by CSB remains unknown. Here we studied CSB's
DNA-binding and
nucleosome-remodeling activities at the single molecule level in real time. We also determined how the NAP1L1 chaperone modulates these activities. We found that CSB interacts with
DNA in two principle ways: by simple binding and a more complex association that involves gross
DNA distortion. Remarkably, NAP1L1 suppresses both these interactions. Additionally, we demonstrate that
nucleosome remodeling by CSB consists of three distinct phases: activation, translocation and pausing, similar to ACF. Importantly, we found that NAP1L1 promotes CSB-mediated remodeling by accelerating both activation and translocation. Additionally, NAP1L1 increases CSB processivity by decreasing the pausing probability during translocation. Our study, therefore, uncovers the different steps of CSB-mediated chromatin remodeling that can be regulated by NAP1L1.