Browsing by Author "Liu, Rui"

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    Dynamics of solar eruptive filaments
    (2008) Liu, Rui; Alexander, David
    The solar filament is one of the most important structures that lead to the destabilization of the solar corona, thereby driving the space weather in the Earth space. The dynamics of solar eruptive filaments is crucial for us to understand the physics governing the initiation of coronal mass ejections (CMEs). In this thesis we concentrate on kinking filaments and asymmetric eruptive filaments, which feature unique dynamic evolutions with implication of distinct initiation mechanisms. Kinking filaments with their warped axes are generally regarded as the 'fingerprint' of the MHD helical kink instability. Theoretical/numerical modelings of the kink instability in the solar context have raised a number of interesting issues which can only be fully addressed with detailed observational inputs. Our study on the kink evolution in a number of filament eruptions with a wide range of different natures provide a complete picture of how the kink instability works in the interactions of the filament with its magnetic environment. Our work has shown evidence supporting the writhing motion of the filament spine as a precursor of eruptive phenomena in the solar corona, and as a key component in regulating the nature of the eruption, in terms of full, partial or failed eruptions. The dynamic evolution of both kinking and asymmetric eruptive filaments has significant impacts on the production of hard X-ray emission. We have identified two types of asymmetric eruptive filaments: whipping-like and zipping-like, which are associated with the shifting of hard X-ray sources in different ways. Both can be understood in terms of how the highly sheared filament channel field responds to an external asymmetric magnetic confinement. In kinking filaments, our study suggests that two distinct processes take place during the kink evolution, leading to two types of HXR emission with different morphological connections to the overall magnetic configuration. Self-consistent, qualitative models are constructed in both studies. These results improve our understanding of the physical processes leading to the destabilization and eruption of solar filaments, and have significant impact on the modeling of the CME initiation and evolution.
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    KAT2A coupled with the α-KGDH complex acts as a histone H3 succinyltransferase
    (Springer Nature, 2017) Wang, Yugang; Guo, Yusong R.; Liu, Ke; Yin, Zheng; Liu, Rui; Xia, Yan; Tan, Lin; Yang, Peiying; Lee, Jong-Ho; Li, Xin-jian; Hawke, David; Zheng, Yanhua; Qian, Xu; Lyu, Jianxin; He, Jie; Xing, Dongming; Tao, Yizhi Jane; Lu, Zhimin
    Histone modifications, such as the frequently occurring lysine succinylation1,2, are central to the regulation of chromatin-based processes. However, the mechanism and functional consequences of histone succinylation are unknown. Here we show that the α-ketoglutarate dehydrogenase (α-KGDH) complex is localized in the nucleus in human cell lines and binds to lysine acetyltransferase 2A (KAT2A, also known as GCN5) in the promoter regions of genes. We show that succinyl-coenzyme A (succinyl-CoA) binds to KAT2A. The crystal structure of the catalytic domain of KAT2A in complex with succinyl-CoA at 2.3 Å resolution shows that succinyl-CoA binds to a deep cleft of KAT2A with the succinyl moiety pointing towards the end of a flexible loop 3, which adopts different structural conformations in succinyl-CoA-bound and acetyl-CoA-bound forms. Site-directed mutagenesis indicates that tyrosine 645 in this loop has an important role in the selective binding of succinyl-CoA over acetyl-CoA. KAT2A acts as a succinyltransferase and succinylates histone H3 on lysine 79, with a maximum frequency around the transcription start sites of genes. Preventing the α-KGDH complex from entering the nucleus, or expression of KAT2A(Tyr645Ala), reduces gene expression and inhibits tumour cell proliferation and tumour growth. These findings reveal an important mechanism of histone modification and demonstrate that local generation of succinyl-CoA by the nuclear α-KGDH complex coupled with the succinyltransferase activity of KAT2A is instrumental in histone succinylation, tumour cell proliferation, and tumour development.