Biomod/2012/Titech/Nano-Jugglers/Methods/Dissociation of photoresponsive DNA

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3.2. Achievement of the photo-switchable DNA system

    The duplex-forming activities of DNA can be photomodulated by incorporation of an azobenzene unit[1]. The duplex is dissociated on isomerizing the trans-azobenzene to the cis form by irradiation with UV light. The duplex is formed again when the cis-azobenzene is converted to the transazobenzene by irradiation with visible light.
    We inserted this function into a bead-body and added the photo-switching function to the Biomolecular Rocket.In brief, so that we can detach the engines by irradiation with UV light, we attached engines to the body with DNA duplex incorporating azobenzene unit.

    We measured DNA absorbance and ascertain the duplex-forming and duplex-dissociation activities of photoresponsive DNA sequence S and S*. As the ordered regions of stacked base pairs in the DNA duplex are dissociated, the UV absorbance increases. This difference in absorbance between the duplex and single strand state is the result of nearest neighbor base pair interactions. In other words, when the DNA is in the duplex state, interactions between base pairs decrease the UV absorbance relative to single strands. When the DNA is in the single strand state the interactions are much weaker,due to the decreased proximity, and the UV absorbance is higher than the duplex state. About this time, we analyze the relationship between the time for dissociation of photo-switcable DNA and the strength of the UV light.
[1]Xingguo Liang,Hidenori Nishioka, Nobutaka Takenaka, and Hiroyuki Asanuma,;ChemBioChem 9, 702 – 705(2008)
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