中科院上海生命科学研究院植生生态所植物分子遗传国家重点实验室方玉达研究组通过研究，发现了组蛋白变体H3.3分子中决定其嵌入核小体和从核小体上解离的信号氨基酸。

组蛋白变体嵌入核小体形成了结构和功能各异的核小体，在生物体表观遗传过程中起非常重要的作用。组蛋白H3家族包括H3.1、H3.3和着丝粒特异的CenH3，它们在从果蝇到人类和植物中都非常保守。H3.3主要通过与一些分子伴侣如HIRA、DAXX、ATRX以及DEK等作用，从而代替H3.1与转录活化的染色质结合，在生殖细胞的发育、表观遗传记忆和染色质重塑等方面发挥重要的作用。拟南芥组蛋白H3.3与H3.1只有四个氨基酸的不同，分别是N-端的31和41位以及组蛋白核心区的87和90位。

通过对拟南芥组蛋白H3.3和H3.1及它们的突变蛋白在核仁rDNA上精细的细胞生物学动态分析，方玉达领导的研究组提出和证实了这样一个模型：即处于组蛋白H3.3核心区域的87位和90位氨基酸介导了核小体的组装，而位于N端的31位和41位氨基酸则介导了核小体的去组装。

由于组蛋白变体H3.3及其相关的核小体在不同生物体中的高度保守性，因此该结果具有较广泛的生物学意义。

相关研究论文于6月13日在线发表于美国《国家科学院院刊》（PNAS）。该工作得到了中国科学院知识创新工程、植物分子遗传国家重点实验室、国家自然科学基金等的支持。

原文出处：

Proceedings of the National Academy of Sciences     DOI： 10.1073/pnas.1017882108

Four amino acids guide the assembly or disassembly of Arabidopsis histone H3.3-containing nucleosomes

Shi, Leilei; Wang, Jing; Hong, Fang; Spector, David L.; Fang, Yuda

The histone variant H3.3 and the canonical histone H3.1, which differ in only 4- to 5-aa positions, are coexpressed in complexmulticellular eukaryotes from fly to human and plant. H3.3 is mainly associated with active chromatin by replacing H3.1 throughchaperones such as histone regulator A, death domain associated protein DAXX, thalassemia/mental retardation syndrome X-linkedhomolog ATRX, or proto-oncogene protein DEK and plays important roles in the germline, epigenetic memory, and reprogramming.However, the signals within H3.3 that serve as a guide for its dynamic deposition or depletion in plant chromatin are notclear. Here, we show that Arabidopsis histone H3.3 differs from H3.1 by 4-aa sites: amino acids 31, 41, 87, and 90. Although histone H3.1 is highly enriched inchromocenters, H3.3 is present in nucleolar foci in addition to being diffusely distributed in the nucleoplasm. We have evaluatedthe function of the 4 aa that differ between H3.1 and H3.3. We show that amino acid residue 87, and to some extent residue90, of Arabidopsis histone H3.3 are critical for its deposition into rDNA arrays. When RNA polymerase I-directed nucleolar transcription isinhibited, wild type H3.3, but not H3.3 containing mutations at residues 31 and 41, is depleted from the rDNA arrays. Together,our results are consistent with a model in which amino acids 87 and 90 in the core domain of H3.3 guide nucleosome assembly,whereas amino acids 31 and 41 in the N-terminal tail of Arabidopsis H3.3 guide nucleosome disassembly in nucleolar rDNA.