Choi Eun Shik, Shin Jin A, Kim Hyun Soo, Jang Yeun Kyu
Research Institute, National Cancer Center, 809 Madu-dong, Ilsan-gu, Goyang, Gyeonggi 411-764, Republic of Korea.
Nucleic Acids Res. 2005 Dec 15;33(22):7102-10. doi: 10.1093/nar/gki1011. Print 2005.
Recently, a histone H3 variant in Drosophila and humans, the H3.3 protein, was shown to replace canonical H3 in active chromatin in a replication-independent (RI) manner. In the fission yeast Schizosaccharomyces pombe, there exists a single form of H3, which is equivalent to H3.3 and is thought to participate in both replication-independent (RI) and replication-coupled (RC) nucleosome assembly. In this study, we show that RI deposition of H3 at heterochromatic regions is consistently lower than that at a gene-free euchromatic region, and deletion of the conserved heterochromatin-specific proteins Swi6 or Clr4 markedly increases RI deposition at heterochromatic regions such as the silent mating-type loci or centromeres. These results clearly show that RI deposition of H3 occurs preferentially in euchromatic regions. We also observed that RI deposition of H3 could be increased at the thi3(+) gene when transcription is induced, indicating transcription further facilitates RI deposition of H3. Taken together, these observations demonstrate that selective deposition of histone H3.3 at transcriptionally active chromatin by the RI assembly pathway is conserved in fission yeast and, thus, our data support an essential role of histone H3 replacement in maintaining active chromatin among diverse eukaryotic organisms ranging from fission yeast to humans.
最近,果蝇和人类中的一种组蛋白H3变体,即H3.3蛋白,被证明以不依赖复制(RI)的方式取代活性染色质中的经典H3。在裂殖酵母粟酒裂殖酵母中,存在单一形式的H3,它等同于H3.3,并且被认为参与不依赖复制(RI)和与复制偶联(RC)的核小体组装。在本研究中,我们表明H3在异染色质区域的RI沉积始终低于在无基因常染色质区域的沉积,并且缺失保守的异染色质特异性蛋白Swi6或Clr4会显著增加在诸如沉默交配型位点或着丝粒等异染色质区域的RI沉积。这些结果清楚地表明H3的RI沉积优先发生在常染色质区域。我们还观察到,当诱导转录时,H3在thi3(+)基因处的RI沉积会增加,表明转录进一步促进H3的RI沉积。综上所述,这些观察结果表明,通过RI组装途径在转录活性染色质上选择性沉积组蛋白H3.3在裂殖酵母中是保守的,因此,我们的数据支持组蛋白H3替代在从裂殖酵母到人类的各种真核生物中维持活性染色质方面的重要作用。
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