期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：43
页码：E5787-E5795
DOI：10.1073/pnas.1508371112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceOn the majority of eukaryotic genes RNA polymerase II meets nucleosomes during transcription of every [~]200 bp of DNA. The key features of Pol II-nucleosome encounter are conserved from yeast to human, but the molecular mechanism of this process remains unknown. Our data suggest a mechanism of formation of the high nucleosomal barrier to Pol II that participates in regulation of transcript elongation in eukaryotes. The proposed mechanism explains the remarkable efficiency of nucleosome survival during transcription, important for maintenance of epigenetic and regulatory histone modifications. Similar mechanisms are likely used during various other DNA transactions, including DNA replication and ATP-dependent chromatin remodeling. Some factors involved in chromatin transcription (e.g., FACT and PARP) participate in cancer development/aging. Thousands of human and Drosophila genes are regulated at the level of transcript elongation and nucleosomes are likely targets for this regulation. However, the molecular mechanisms of formation of the nucleosomal barrier to transcribing RNA polymerase II (Pol II) and nucleosome survival during/after transcription remain unknown. Here we show that both DNA-histone interactions and Pol II backtracking contribute to formation of the barrier and that nucleosome survival during transcription likely occurs through allosterically stabilized histone-histone interactions. Structural analysis indicates that after Pol II encounters the barrier, the enzyme backtracks and nucleosomal DNA recoils on the octamer, locking Pol II in the arrested state. DNA is displaced from one of the H2A/H2B dimers that remains associated with the octamer. The data reveal the importance of intranucleosomal DNA-protein and protein-protein interactions during conformational changes in the nucleosome structure on transcription. Mechanisms of nucleosomal barrier formation and nucleosome survival during transcription are proposed.
