Doyen Cécile-Marie, Montel Fabien, Gautier Thierry, Menoni Hervé, Claudet Cyril, Delacour-Larose Marlène, Angelov Dimitri, Hamiche Ali, Bednar Jan, Faivre-Moskalenko Cendrine, Bouvet Philippe, Dimitrov Stefan
Institut Albert Bonniot, INSERM U309, La Tronche cedex, France.
EMBO J. 2006 Sep 20;25(18):4234-44. doi: 10.1038/sj.emboj.7601310. Epub 2006 Sep 7.
The histone variant H2A.Bbd appeared to be associated with active chromatin, but how it functions is unknown. We have dissected the properties of nucleosome containing H2A.Bbd. Atomic force microscopy (AFM) and electron cryo-microscopy (cryo-EM) showed that the H2A.Bbd histone octamer organizes only approximately 130 bp of DNA, suggesting that 10 bp of each end of nucleosomal DNA are released from the octamer. In agreement with this, the entry/exit angle of the nucleosomal DNA ends formed an angle close to 180 degrees and the physico-chemical analysis pointed to a lower stability of the variant particle. Reconstitution of nucleosomes with swapped-tail mutants demonstrated that the N-terminus of H2A.Bbd has no impact on the nucleosome properties. AFM, cryo-EM and chromatin remodeling experiments showed that the overall structure and stability of the particle, but not its property to interfere with the SWI/SNF induced remodeling, were determined to a considerable extent by the H2A.Bbd docking domain. These data show that the whole H2A.Bbd histone fold domain is responsible for the unusual properties of the H2A.Bbd nucleosome.
组蛋白变体H2A.Bbd似乎与活性染色质相关,但其功能尚不清楚。我们剖析了含有H2A.Bbd的核小体的特性。原子力显微镜(AFM)和冷冻电子显微镜(cryo-EM)显示,H2A.Bbd组蛋白八聚体仅组装约130 bp的DNA,这表明核小体DNA两端各有10 bp从八聚体中释放出来。与此一致的是,核小体DNA末端的进出角形成接近180度的角度,物理化学分析表明变体颗粒的稳定性较低。用交换尾巴突变体重建核小体表明,H2A.Bbd的N末端对核小体特性没有影响。AFM、cryo-EM和染色质重塑实验表明,颗粒的整体结构和稳定性,而非其干扰SWI/SNF诱导的重塑的特性,在很大程度上由H2A.Bbd对接结构域决定。这些数据表明,整个H2A.Bbd组蛋白折叠结构域决定了H2A.Bbd核小体的异常特性。