Biophysical Society Thematic Meeting - October 25-30, 2015

Polymers and Self Assembly: From Biology to Nanomaterials Poster Session II

27-POS Board 27 Viscoelastic Properties of DNA in Vivo Measured by Fluorescence Correlation Spectroscopy Rudra Kafle, Liebeskind Molly, Jens-christian Meiners . University of Michigan, Ann Arbor, USA. Mechanical quantities like the elasticity of cells are conventionally measured by directly probing them mechanically. This, however, is often impractical, and even impossible when subcellular structures inside living cells are concerned. We use a purely optical method instead; an adaptation of fluorescence correlation spectroscopy (FCS) to measure such mechanical quantities in chromosomal DNA in live E. Coli cells. FCS is a fluorescence technique conventionally used to study the kinetics of fluorescent molecules in a dilute solution. Being a non-invasive technique, it is now drawing increasing interest for the study of more complex systems like the dynamics of DNA or proteins in living cells and cell membranes. Unlike an ordinary dye solution, the dynamics of macromolecules like proteins or entangled DNA in crowded environments is often slow and subdiffusive in nature. This in turn leads to longer residence times of the attached fluorophores in the excitation volume of the microscope and artifacts from photobleaching abound that can easily obscure the signature of the molecular dynamics of interest. We present a method of calculating the intensity autocorrelation function from the arrival times of the photons on the detector that maximizes the information content while correcting for the effect of photobleaching to yield an autocorrelation function that reflects only the underlying dynamics of the sample. This autocorrelation function in turn is used to calculate the mean square displacement of the fluorophores attached to DNA. By using a suitable integral transform of the mean square displacement, we determine the viscoelastic moduli for lambda- DNA solution and the DNA in E. coli. We note that these mechanical quantities evaluated by an optical technique are in good agreement with similar quantities measured by completely different techniques.

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