| 报告题目 | A Novel Hybrid Single Molecule Approach Reveals Spontaneous DNA Motion in the Nucleosome |
| 报告人 | Dr. WEI Sijie |
| 报告人单位 | Department of Chemistry, The Pennsylvania State University |
| 报告时间 | 2015-05-22 |
| 报告地点 | 合肥微尺度物质科学国家实验室（9004室） |
| 主办单位 | 合肥微尺度物质科学国家实验室 |
| 报告介绍 | Abstract:
The nucleosome, comprising DNA and an octameric histone protein core, is the fundamental packing unit of eukaryotic genes that must be accessed and processed by factors and polymerases during various genome transactions such as transcription, replication, and DNA repair. Spontaneous DNA opening motion at the nucleosome termini has long been hypothesized to enable gene access during these processes. However, direct observation of this motion has never been reported likely because it is too fast to be monitored with the currently available methods. Unsynchronized dynamics in the structures of nucleic acid and protein can be efficiently monitored with single molecule fluorescence methods such as single molecule FRET (smFRET)whose time-resolution can be improved by stochastic data analysis. One such approach is to optimize time resolved FRET dynamics according to the sequence of fluorescence photon emission intervals based on maximum likelihood estimation (MLE). This type of analysis with small signal changes, however, often yields extremely large uncertainty, making the confidence in the results unacceptably low. This is because the analysis is often trapped in a local maximum likelihood and there is no practical means to resolve this issue from an analytical approach. In order to address this problem, we combined fluorescence correlation spectroscopy (FCS) with MLE-based data analysis that enables investigations of unsynchronized structural dynamics of macromolecules.
Based on the method, we report the first direct evidence of spontaneous DNA motions at the nucleosome termini and its quantitative characteristics. Our approach reveals that DNA termini in the nucleosome open and close repeatedly at 0.1~1ms-1, which imposes the kinetic limit to gene access. The kinetics depends on salt concentration and DNA-histone interactions but not much on DNA sequence, suggesting that this dynamics is universal. These results clearly demonstrate that our method provides an efficient and robust means to investigate unsynchronized sub-nm structural changes at a sub-ms time resolution, and will greatly help elucidate the physical mechanism of gene access at the molecular level. |
