Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, MD, USA.
Department of Biology, Johns Hopkins University, Baltimore, MD, USA.
Sci Adv. 2022 Mar 11;8(10):eabj5509. doi: 10.1126/sciadv.abj5509. Epub 2022 Mar 9.
Nucleosomal histone H2A is exchanged for its variant H2A.Z by the SWR1 chromatin remodeler, but the mechanism and timing of histone exchange remain unclear. Here, we quantify DNA and histone dynamics during histone exchange in real time using a three-color single-molecule FRET assay. We show that SWR1 operates with timed precision to unwrap DNA with large displacement from one face of the nucleosome, remove H2A-H2B from the same face, and rewrap DNA, all within 2.3 s. This productive DNA unwrapping requires full SWR1 activation and differs from unproductive, smaller-scale DNA unwrapping caused by SWR1 binding alone. On an asymmetrically positioned nucleosome, SWR1 intrinsically senses long-linker DNA to preferentially exchange H2A.Z on the distal face as observed in vivo. The displaced H2A-H2B dimer remains briefly associated with the SWR1-nucleosome complex and is dissociated by histone chaperones. These findings reveal how SWR1 coordinates DNA unwrapping with histone dynamics to rapidly and accurately place H2A.Z at physiological sites on chromatin.
核小体组蛋白 H2A 可被 SWR1 染色质重塑酶交换为其变体 H2A.Z，但组蛋白交换的机制和时间仍不清楚。在这里，我们使用三色单分子 FRET 测定法实时定量研究了组蛋白交换过程中的 DNA 和组蛋白动力学。我们表明，SWR1 以定时精度从核小体的一个面解开具有大位移的 DNA，从同一面去除 H2A-H2B，并重新缠绕 DNA，所有这些都在 2.3 秒内完成。这种有生产力的 DNA 解缠绕需要完全激活 SWR1，与仅由 SWR1 结合引起的无生产力、较小规模的 DNA 解缠绕不同。在不对称定位的核小体上，SWR1 内在地感知长连接 DNA，以优先在远端面交换 H2A.Z，就像在体内观察到的那样。移位的 H2A-H2B 二聚体与 SWR1-核小体复合物短暂相关，并被组蛋白伴侣解离。这些发现揭示了 SWR1 如何协调 DNA 解缠绕与组蛋白动力学，以快速准确地将 H2A.Z 放置在染色质上的生理部位。
