Construction of photoresponsive RNA for photoswitching RNA hybridization.

By introducing azobenzenes into RNA using d-threoninol as a scaffold, a photoresponsive RNA was constructed for efficiently photoswitching the formation and dissociation of RNA/RNA duplexes. The difference in melting temperature (T(m)) between the trans and cis forms was so large that efficient photoregulation of RNA hybridization became possible, irrespective of the sequence adjacent to the introduced azobenzene. Compared to the corresponding photoresponsive DNA, the photoregulatory efficiency of azobenzene-modified RNA was even higher due to the drastic destabilization by cis-azobenzene. Structural analysis by NMR and molecular modeling indicated that the planar trans-azobenzene could not stabilize the RNA/RNA duplex with a rigid A-form structure by base pair stacking. However, the large steric hindrance caused by nonplanar cis-azobenzene was quite effective at distorting and destabilizing the duplex structure. We also discuss the effect of methylation of azobenzene at the ortho positions on photoregulation of RNA/RNA duplex formation. This newly constructed photoresponsive RNA has promising applications such as photoswitching of RNA functions.