Ho Cheng-Han, Nozawa Kayo, Nishimura Masahiro, Oi Mayuko, Kujirai Tomoya, Ogasawara Mitsuo, Ehara Haruhiko, Sekine Shun-Ichi, Takizawa Yoshimasa, Kurumizaka Hitoshi
Laboratory of Chromatin Structure and Function, Institute for Quantitative Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
bioRxiv. 2025 May 13:2025.05.13.653634. doi: 10.1101/2025.05.13.653634.
The H3-H4 octasome is a nucleosome-like particle in which two DNA gyres are wrapped around each H3-H4 tetramer disk, forming a clamshell-like configuration. In the present study, we performed in vitro RNAPII transcription assays with the H3-H4 octasome and found that RNAPII transcribed the H3-H4 octasome more efficiently than the nucleosome. RNAPII paused at only one position, superhelical location (SHL) -4 in the H3-H4 octasome, in contrast to pausing at the SHL(-5), SHL(-2), and SHL(-1) positions in the nucleosome. Cryo-electron microscopy analysis revealed that two H3-H4 tetramer disks are retained when the RNAPII paused at the SHL(-4) position of the H3-H4 octasome. However, when RNAPII reached the SHL(-0.5) position, five base pairs before the dyad position of the H3-H4 octasome, the proximal H3-H4 tetramer was disassembled but the distal H3-H4 tetramer still remained on the DNA. Therefore, RNAPII efficiently transcribes the H3-H4 octasome by stepwise H3-H4 tetramer disassembly.
H3-H4八聚体是一种核小体样颗粒，其中两个DNA螺旋缠绕在每个H3-H4四聚体盘周围，形成蛤壳状结构。在本研究中，我们用H3-H4八聚体进行了体外RNA聚合酶II（RNAPII）转录试验，发现RNAPII转录H3-H4八聚体的效率高于核小体。RNAPII仅在H3-H4八聚体的一个位置，即超螺旋位置（SHL）-4处暂停，这与在核小体的SHL（-5）、SHL（-2）和SHL（-1）位置暂停形成对比。冷冻电子显微镜分析显示，当RNAPII在H3-H4八聚体的SHL（-4）位置暂停时，两个H3-H4四聚体盘得以保留。然而，当RNAPII到达H3-H4八聚体二分位置前五个碱基对的SHL（-0.5）位置时，近端H3-H4四聚体被拆解，但远端H3-H4四聚体仍保留在DNA上。因此，RNAPII通过逐步拆解H3-H4四聚体有效地转录H3-H4八聚体。
