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Characterizing highly dynamic conformational states: The transcription bubble in RNAP-promoter open complex as an example.

ABSTRACT: Bio-macromolecules carry out complicated functions through structural changes. To understand their mechanism of action, the structure of each step has to be characterized. While classical structural biology techniques allow the characterization of a few "structural snapshots" along the enzymatic cycle (usually of stable conformations), they do not cover all (and often fast interconverting) structures in the ensemble, where each may play an important functional role. Recently, several groups have demonstrated that structures of different conformations in solution could be solved by measuring multiple distances between different pairs of residues using single-molecule Förster resonance energy transfer (smFRET) and using them as constrains for hybrid/integrative structural modeling. However, this approach is limited in cases where the conformational dynamics is faster than the technique's temporal resolution. In this study, we combine existing tools that elucidate sub-millisecond conformational dynamics together with hybrid/integrative structural modeling to study the conformational states of the transcription bubble in the bacterial RNA polymerase-promoter open complex (RPo). We measured microsecond alternating laser excitation-smFRET of differently labeled lacCONS promoter dsDNA constructs. We used a combination of burst variance analysis, photon-by-photon hidden Markov modeling, and the FRET-restrained positioning and screening approach to identify two conformational states for RPo. The experimentally derived distances of one conformational state match the known crystal structure of bacterial RPo. The experimentally derived distances of the other conformational state have characteristics of a scrunched RPo. These findings support the hypothesis that sub-millisecond dynamics in the transcription bubble are responsible for transcription start site selection.

SUBMITTER: Lerner E

PROVIDER: S-EPMC5750056 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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Characterizing highly dynamic conformational states: The transcription bubble in RNAP-promoter open complex as an example.

Lerner Eitan E Ingargiola Antonino A Weiss Shimon S

The Journal of chemical physics 20180301 12

Bio-macromolecules carry out complicated functions through structural changes. To understand their mechanism of action, the structure of each step has to be characterized. While classical structural biology techniques allow the characterization of a few "structural snapshots" along the enzymatic cycle (usually of stable conformations), they do not cover all (and often fast interconverting) structures in the ensemble, where each may play an important functional role. Recently, several groups have ...[more]

PMID: 29604842

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Project description:Serum-to-2i interconversion of mouse Embryonic Stem Cells (mESCs) is a valuable in vitro model for early embryonic development. To assess whether 3D chromatin organization changes during this transition, we established Capture Hi-C with target-sequence enrichment of DNase I hypersensitive sites. We detected extremely long-range intra- and inter-chromosomal interactions between a small subset of H3K27me3 marked bivalent promoters involving the Hox clusters in serum grown cells. Notably, these promoter-mediated interactions are not present in 2i ground-state pluripotent mESCs but appear upon further development into primed-like serum mESCs. Reverting serum mESCs to ground-state 2i mESCs removes these promoter-promoter interactions in a spatiotemporal manner. H3K27me3, which is largely absent at bivalent promoters in ground-state 2i mESCs, is necessary but not sufficient to establish these interactions, as confirmed by Capture Hi-C on Eed-/- serum mESCs. Our results implicate H3K27me3 and PRC2 as critical players in chromatin alteration during priming of ESCs for differentiation. To study dynamics in chromatin architecture and to characterize long-range interaction, we performed Hi-C using DpnII as the restriction enzyme, potentially reaching a genome-wide coverage at a less than 1Kb resolution. We subsequently performed enrichment of interaction by a target capture similar to the exome sequencing approach. We enriched for DNaseI hyper-sensitive sites (DHSâs) in chromatin from mESCs. Probes were designed against the union of all DHSâs of Serum and 2i mESCs. Capture Hi-C reveals Extremely Long-Range Interactions (ELRI) in Serum but not in 2i ESCs. We observed H3K27me3 as a prominent characteristic, but not exclusive feature of ELRI loci in Serum mESCs. To further elucidate the involvement of constituents of PRC1 and PRC2 in ELRI, we performed ChIP-seq experiment on Suz12 and Ring1B during serum-to-2i transition. In addition, RNA-seq was performed to compare the expression levels of genes.

Dataset Information

Characterizing highly dynamic conformational states: The transcription bubble in RNAP-promoter open complex as an example.

Publications

Characterizing highly dynamic conformational states: The transcription bubble in RNAP-promoter open complex as an example.

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