The human BAF chromatin remodeler processes nucleosomes bound by pioneer transcription factors OCT4-SOX2.

Chromatin remodeling complexes mobilize nucleosomes and promote transcription factor (TF) binding. Using ensemble and single-molecule assays combined with cryo-electron microscopy (cryo-EM), we studied the interaction between pioneer TFs OCT4-SOX2 and the human BRG1/BRM-associated factor (BAF) complex on nucleosomes. BAF engages TF-bound substrates in two orientations, placing OCT4-SOX2 at either the remodeler ENTRY or EXIT site. At the ENTRY site, OCT4-SOX2 initially coexists with BAF without structural interference. However, continued DNA translocation is expected to cause collisions with bound TFs, which can trigger remodeling direction reversals or may induce TF dissociation. To accommodate TFs at the EXIT site, BAF undergoes structural rearrangements, and ensemble assays reveal a nucleosome subpopulation translocating away from TF-binding sites. Moreover, single-molecule experiments show that nucleosome-bound BAF frequently changes remodeling direction, and we identify an ADP-bound remodeler conformation as a potential intermediate. Together, these findings reveal key aspects of the conformational dynamics and remodeling outcomes underlying BAF processing of TF-bound nucleosomes.