A supra-photoswitch is designed for complete ON/OFF switching of DNA hybridization by light irradiation for the purpose of using DNA as a material for building nanostructures. Azobenzenes, attached to D-threoninols that function as scaffolds, are introduced into each DNA strand after every two natural nucleotides (in the form (NNX)n where N and X represent the natural nucleotide and the azobenzene moiety, respectively). Hybridization of these two modified strands forms a supra-photoswitch consisting of alternating natural base pairs and azobenzene moieties. In this newly designed sequence, each base pair is sandwiched between two azobenzene moieties and all the azobenzene moieties are separated by base pairs. When the duplex is irradiated by visible light, the azobenzene moieties take the trans form and this duplex is surprisingly stable compared to the corresponding native duplex composed of only natural oligonucleotides. On the other hand, when the azobenzene moieties are isomerized to the cis form by UV light irradiation, the duplex is completely dissociated. Based on this design, a DNA hairpin structure is synthesized that should be closed by visible light irradiation and opened by UV light irradiation at the level of a single molecule. Indeed, perfect ON/OFF photoregulation is attained. This is a promising strategy for the design of supra-photoswitches such as photoresponsive sticky ends on DNA nanodevices and other nanostructures.

Various three-dimensional structures have been created on a nanometer scale using the self-assembly of DNA molecules. However, ordinary DNA structures breakdown readily because of their flexibility. In addition, it is difficult to control them by inputs from environments. Here, we construct robust and photocontrollable DNA capsules using azobenzenes. This provides a method to construct DNA structures that can survive higher temperatures and can be controlled with ultraviolet irradiation.

Recently, DNA has gained attention as one of the most promising molecules for use in bottom-up nanotechnology. [1] In the last two decades, numerous DNA nanostructures with mechanical functions such as DNA tweezers, DNA walkers, and DNA gears have been constructed. [2,3] However, the practical use of DNA nanotechnology remains a great challenge. One of the problems limiting the application of DNA nanomachines is that oligo-DNAs or other small molecules have to be added as the "fuel" during each operation cycle, and "waste" molecules detrimentally accumulate in the system after several cycles.[3] Previously, we have tried to solve this problem by constructing a model photon-fueled nanomachine involving azobenzene moieties as photoswitches, based on the photoregulation of DNA hybridization. [4,5] No waste was produced because only light, the cleanest source of energy, was used to drive the nanomachine, and the operation could be repeated for many cycles without loss of efficiency.[4a] Efforts should be made to construct nanomachines that work on the single-molecule level, which is highly favorable for nanotechnology applications.[4c] In the present study, we constructed a machinelike photoresponsive DNAzyme that can work at the singlemolecule level (intramolecular nanomachine). The change of its topological conformation can be regulated simply by light irradiation. For the first time, complete ON-OFF photoswitching of RNA digestion has been realized by regulating the higher order structure of a DNAzyme-RNA complex.The 10-23 DNAzyme, captured from a DNA pool of random sequences by in vitro selection, was used here as the model system for constructing an RNA-cleaving nanomachine driven by photons.[6] As shown in Scheme 1 a, a photoresponsive machinelike DNAzyme (Dz7X) was constructed by attaching complementary azobenzene-modified sequences to both ends of the 10-23 DNAzyme. As in our previous design, the two azobenzene-modified sequences were able to form an interstrand-wedged duplex after hybridization. [4c,d] When visible light is applied, the azobenzene residues (X) take the trans form, and a very stable duplex structure involving seven azobenzene units and nine base pairs is formed.[4c] The modified DNAzyme Dz7X can be regarded as a DNA hairpin structure with a big loop (Scheme 1 a). In this case, the RNA-cleavage activity is expected to be suppressed because the topologically constrained higher order structure of the catalytic loop cannot form the correct conformation for cleavage, even when the RNA substrate hybridizes with both arms. On the other hand, when UV light is applied and azobenzene residues take the cis Scheme 1. Design of the machinelike photoresponsive DNAzyme (a) and sequences of DNAzymes and RNA targets used in this study (b). The azobenzene-modified DNAzymes show high activity only when azobenzenes (in red; its structure (X) is also shown) take the cis form after irradiation with UV light. RNA substrate (in green) was labeled with the fluorophore FITC at the 5' end. The sequence of catalytic lo...

Figure 3. Photoswitching of RNA cleavage at the GU site by Dz7X. Visible light was applied at 0, 60, 120, and 180 min. UV light irradiation was carried out at 30, 90, and 150 min. The irradiation time for visible and UV light was 1 and 10 min, respectively. Figure 4. Effect of the topological constraint on RNA digestion by the 10-23 DNA enzyme (see sequences in Scheme 1 b).

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This paper describes the development of a software program that supports argumentative reading and writing, especially for novice students. The software helps readers create a graphic organizer from the text as a knowledge map while they are reading and use their prior knowledge to build their own opinion as new information while they think about writing their essays. Readers using this software can read a text, underline important words or sentences, pick up and dynamically cite the underlined portions of the text onto a knowledge map as quotation nodes, illustrate a knowledge map by linking the nodes, and later write their opinion as an essay while viewing the knowledge map; thus, the software bridges argumentative reading and writing. Sixty-three freshman and sophomore students with no prior argumentative reading and writing education participated in a design case study to evaluate the software in classrooms. Thirty-four students were assigned to a class in which each student developed a knowledge map after underlining and/or highlighting a text with the software, while twenty-nine students were assigned to a class in which they simply wrote their essays after underlining and/or highlighting the text without creating knowledge maps. After receiving an instruction regarding a simplified Toulmin's model followed by instructions for the software usage in argumentative reading and writing along with reading one training text, the students read the target text and developed their essays. The results revealed that students who drew a knowledge map based on the underlining and/or highlighting of the target text developed more argumentative essays than those who did not draw maps. Further analyses revealed that developing knowledge maps fostered an ability to capture the target text's argument, and linking students' ideas to the text's argument directly on the knowledge map helped students develop more constructive essays. Accordingly, we discussed additional necessary scaffolds, such as automatic argument detection and collaborative learning functions, for improving the students' use of appropriate reading and writing strategies.

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