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Detection of Single-Molecule Optical Absorption at Room Temperature and Mechanistic Study of Transcriptional Bursting
Detection of Single-Molecule Optical Absorption at Room Temperature and Mechanistic Study of Transcriptional Bursting
教师介绍

本讲教师:种莎莎
所属学科:理科
人  气:167

课程介绍
Abstract: Advances in optical imaging techniques have allowed quantitative studies of many biological systems. I will talk about my PhD thesis work that was devoted to both developing novel imaging modalities and applying high-sensitivity fluorescence microscopy to the study of biology. Although fluorescence is the most widely used optical contrast mechanism in biological studies because of its background-free detection, many intracellular molecules are intrinsically non-fluorescent and difficult to label without disturbing their natural functions. Therefore, label-free imaging methods based on contrast mechanisms other than fluorescence are highly desirable. The first part of my talk will focus on high-sensitivity detection of optical absorption. This was challenging because a small absorption signal, not spectrally separated from the excitation light, can be buried in the laser intensity noise and often complicated by Rayleigh scattering of the sample. I developed ground-state depletion microscopy based on a high-frequency dual-beam modulation transfer scheme, and achieved detection of the absorption signal from a single molecule at room temperature with shot-noise limited sensitivity. This measurement represents the ultimate detection sensitivity of nonlinear optical spectroscopy at room temperature. In the second part of my talk, I will focus on the mechanism of transcriptional bursting. Transcription of highly expressed genes occurs in stochastic bursts in bacteria, but the origin of this ubiquitous phenomenon had not been understood previously. I developed a high-throughput in vitro single-molecule assay based on fluorescence microscopy to follow transcription on individual DNA templates in real time. With this assay, I found that positive supercoiling buildup on a DNA segment by transcription slows down transcription elongation and eventually stops transcription initiation. Transcription can be resumed upon gyrase binding to the DNA segment. Furthermore, with single-molecule mRNA fluorescence in situ hybridization (FISH) assay, we found that the extent of transcriptional bursting depends on the intracellular gyrase concentration. Together, these findings proved that transcriptional bursting of highly expressed genes in bacteria is primarily caused by reversible gyrase dissociation from and rebinding to a DNA segment, changing the supercoiling level of the segment. 个人简介: 种莎莎博士2008年在科大化学系获得学士学位 (0419郭沫若奖学金获得者); 2014年获得哈佛大学化学与化学生物学博士学位,导师是美国科学院院士谢晓亮博士; 目前在加州大学伯克利分校任博士后研究员,导师是美国科学院院士、霍华德·休斯医学研究所 (HHMI) 主席 Robert Tjian(钱泽南)。 种莎莎博士主要运用物理和化学的手段研究单子分子光谱和利用单分子科学研究生物体系, 工作发表在Cell等杂志上,并被Science,Nature等学术期刊以及世界其它媒体广泛报道。欢迎对物理、生物和化学感兴趣的师生前来参加。

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admin: 发布时间:2017-01-12 10:46
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