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FACT caught in the act of manipulating the nucleosome 期刊论文
NATURE, 2020, 577 (7790) : 426-+
作者:  Shen, Helen
收藏  |  浏览/下载:14/0  |  提交时间:2020/07/03

The organization of genomic DNA into nucleosomes profoundly affects all DNA-related processes in eukaryotes. The histone chaperone known as '  facilitates chromatin transcription'  (FACT(1)) (consisting of subunits SPT16 and SSRP1) promotes both disassembly and reassembly of nucleosomes during gene transcription, DNA replication and DNA repair(2). However, the mechanism by which FACT causes these opposing outcomes is unknown. Here we report two cryo-electron-microscopic structures of human FACT in complex with partially assembled subnucleosomes, with supporting biochemical and hydrogen-deuterium exchange data. We find that FACT is engaged in extensive interactions with nucleosomal DNA and all histone variants. The large DNA-binding surface on FACT appears to be protected by the carboxy-terminal domains of both of its subunits, and this inhibition is released by interaction with H2A-H2B, allowing FACT-H2A-H2B to dock onto a complex containing DNA and histones H3 and H4 (ref. (3)). SPT16 binds nucleosomal DNA and tethers H2A-H2B through its carboxy-terminal domain by acting as a placeholder for DNA. SSRP1 also contributes to DNA binding, and can assume two conformations, depending on whether a second H2A-H2B dimer is present. Our data suggest a compelling mechanism for how FACT maintains chromatin integrity during polymerase passage, by facilitating removal of the H2A-H2B dimer, stabilizing intermediate subnucleosomal states and promoting nucleosome reassembly. Our findings reconcile discrepancies regarding the many roles of FACT and underscore the dynamic interactions between histone chaperones and nucleosomes.


  
Base-pair conformational switch modulates miR-34a targeting of Sirt1 mRNA 期刊论文
NATURE, 2020, 583 (7814) : 139-+
作者:  Muniz, Juan A.;  Barberena, Diego;  Lewis-Swan, Robert J.;  Young, Dylan J.;  Cline, Julia R. K.;  Rey, Ana Maria;  Thompson, James K.
收藏  |  浏览/下载:57/0  |  提交时间:2020/07/03

MicroRNAs (miRNAs) regulate the levels of translation of messenger RNAs (mRNAs). At present, the major parameter that can explain the selection of the target mRNA and the efficiency of translation repression is the base pairing between the '  seed'  region of the miRNA and its counterpart mRNA(1). Here we use R-1 rho relaxation-dispersion nuclear magnetic resonance(2) and molecular simulations(3) to reveal a dynamic switch-based on the rearrangement of a single base pair in the miRNA-mRNA duplex-that elongates a weak five-base-pair seed to a complete seven-base-pair seed. This switch also causes coaxial stacking of the seed and supplementary helix fitting into human Argonaute 2 protein (Ago2), reminiscent of an active state in prokaryotic Ago(4,5). Stabilizing this transient state leads to enhanced repression of the target mRNA in cells, revealing the importance of this miRNA-mRNA structure. Our observations tie together previous findings regarding the stepwise miRNA targeting process from an initial '  screening'  state to an '  active'  state, and unveil the role of the RNA duplex beyond the seed in Ago2.


Repression of a messenger RNA by a cognate microRNA depends not only on complementary base pairing, but also on the rearrangement of a single base pair, producing a conformation that fits better within the human Ago2 protein.


  
A probabilistic approach for attributing temperature changes to synoptic type frequency 期刊论文
INTERNATIONAL JOURNAL OF CLIMATOLOGY, 2017, 37 (6)
作者:  Nilsen, Irene B.;  Stagge, James H.;  Tallaksen, Lena M.
收藏  |  浏览/下载:11/0  |  提交时间:2019/04/09
temperature  trend detection  trend attribution  atmospheric circulation  within-type changes  probabilistic approach  dynamic causes  thermodynamic causes