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. Author manuscript; available in PMC: 2023 Jun 1.
Published in final edited form as: Immunol Rev. 2021 Mar 7;300(1):100–124. doi: 10.1111/imr.12954

Fig. 4. Spontaneous topological deformations of nucleosomes might facilitate passive entry of TFs into occluded cis-regulatory DNA.

Fig. 4.

(A) The fully wrapped state of DNA in a nucleosome is transient (left). Spontaneous unwrapping that begins at the DNA entry and exit locations on the nucleosome occurs ~ 4 times per second. The DNA rewraps very fast, as the unwrapped lifespan is only 10–50 ms. However, transcription factor binding is considered nearly instantaneous, allowing TFs to have many opportunities to access their recognition sites in otherwise nucleosome-occluded sequences (right). Transient activation of bZIP family member TFs (and other TFs, e.g., RHD) in response to TCR stimuli facilitates bZIP and Runx-family TFs to capture transiently accessible nucleosome-DNA and prevent rewrapping. Stable remodelling might require additional chromatin remodelling activities that are delivered by the TFs, or might only depend on cooperative binding by multiple TFs.