Photo-control, the use of ultraviolet or visible light to control a reaction, has a number of advantages over other external stimuli:
Light does not introduce contaminants into the reaction system,
Excitation wavelength can be controlled through the design of the photo-responsive molecule, and
It is now straightforward to control irradiation time and/or local excitation.
When a photo-responsive molecule is directly attached to DNA as a receptor, photo-regulation of the bioprocess regulated by that DNA molecule could, in principle, be achieved. Such photo-responsive DNA could also be used as a switch in a DNA-based nano-machine. Professor Hiroyuki Asanuma and his group at the department of Molecular Design and Engineering of the Graduate School of Engineering of the Nagoya University (Japan) have developed an efficient method to achieve this goal. They have attached azobenzene to DNA and made it photo-responsive1,2. Azobenzene is a typical photo-responsive molecule that isomerizes from its planar trans-form to the non-planar cis-form after UV-light irradiation with a wavelength between 300 nm and 400 nm (lmax is around 330 nm). Interestingly, the system reverts from the cis-form to the trans-form after further irradiation with visible light (wavelength over 400 nm). This process is completely reversible, and the azobenzene group does not decompose or induce undesirable side reactions even on repeated trans-cis isomerization. By introducing azobenzenes into DNA through D-threoninol as a linker, Asanuma and co-workers succeeded in achieving photo-regulation of:
Formation and dissociation of a DNA duplex3,4 and
Transcription by T7-RNA polymerase reaction5,6,7.
H. Asanuma, et al., Angew Chem Int Ed, 2001, 40, 2671-2673.
T. Takarada, et al., Chem Lett., 2001, 30, 732.
H. Asanuma, X.G. Liang, T. Yoshida, and M. Komiyama, Chembiochem, 2001, 2, 39-44.
H. Asanuma, D. Matsunaga, and M. Komiyama, NUCLEIC ACIDS SYMP SER (OXF), 2005, 49, 35.
H. Asanuma, et al., Chembiochem, 2002, 3, 786.
M. Liu, H. Asanuma, and M. Komiyama, J. Amer. Chem. Soc., 2006 , 128, 1009.
H. Asanuma, et al., Nature Protocols, 2007, 2, 203-212..