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30 May 2005

Volume 86, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 86, 223902 (2005); http://dx.doi.org/10.1063/1.1938253 (3 pages)

Philip J. Lee, Paul J. Hung, Robin Shaw, Lily Jan, and Luke P. Lee
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All-or-none switching of transcriptional activity on single DNA molecules caused by a discrete conformational transition

Ayako Yamada, Koji Kubo, Tonau Nakai, Kenichi Yoshikawa, and Kanta Tsumoto

Appl. Phys. Lett. 86, 223901 (2005); http://dx.doi.org/10.1063/1.1937990 (3 pages) | Cited 7 times

Online Publication Date: 25 May 2005

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Recently, it has been confirmed that long duplex DNA molecules with a size larger than several tens of kilo-base pairs (kbp), exhibit a discrete conformational transition from an unfolded coil state to a folded compact state upon the addition of various kinds of chemical species that usually induce DNA condensation. In this study, we performed a single-molecule observation on a large DNA, Lambda ZAP II DNA ( ∼ 41 kbp), in a solution containing RNA polymerase and substrates along with spermine, a tetravalent cation, at different concentrations, by use of fluorescence staining of both DNA and RNA. We found that transcription, or RNA production, is completely inhibited in the compact globule state, but is actively performed in the unfolded coil state. Such an all-or-none effect on transcriptional activity induced by the discrete conformational transition of single DNA molecules is discussed in relation to the mechanism of the regulation of large-scale genetic activity.
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87.15.H- Dynamics of biomolecules
87.15.M- Spectra of biomolecules
33.50.Dq Fluorescence and phosphorescence spectra

Microfluidic application-specific integrated device for monitoring direct cell-cell communication via gap junctions between individual cell pairs

Philip J. Lee, Paul J. Hung, Robin Shaw, Lily Jan, and Luke P. Lee

Appl. Phys. Lett. 86, 223902 (2005); http://dx.doi.org/10.1063/1.1938253 (3 pages) | Cited 29 times

Online Publication Date: 25 May 2005

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Direct cell-cell communication between adjacent cells is vital for the development and regulation of functional tissues. However, current biological techniques are difficult to scale up for high-throughput screening of cell-cell communication in an array format. In order to provide an effective biophysical tool for the analysis of molecular mechanisms of gap junctions that underlie intercellular communication, we have developed a microfluidic device for selective trapping of cell-pairs and simultaneous optical characterizations. Two different cell populations can be brought into membrane contact using an array of trapping channels with a 2 μm by 2 μm cross section. Device operation was verified by observation of dye transfer between mouse fibroblasts (NIH3T3) placed in membrane contact. Integration with lab-on-a-chip technologies offers promising applications for cell-based analytical tools such as drug screening, clinical diagnostics, and soft-state biophysical devices for the study of gap junction protein channels in cellular communications. Understanding electrical transport mechanisms via gap junctions in soft membranes will impact quantitative biomedical sciences as well as clinical applications.
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87.80.-y Biophysical techniques (research methods)
87.16.Uv Active transport processes
87.16.D- Membranes, bilayers, and vesicles
87.14.E- Proteins
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.17.-d Cell processes
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