Placing Extra Components into RNA by Specific Transcription Using Unnatural Base Pair Systems

RNA molecules, which can be simply prepared and amplified by transcription using DNA templates, display versatile functionalities depending on their sequences and higher-order structures. This characteristic allows us to generate novel species of RNA that bind target molecules (aptamers) and catalysts (ribozymes) by in vitro selection methods using large populations of random RNA sequences. Over the last 15 years, researchers have created many aptamers and ribozymes for their purposes. Consequently, a modified RNA aptamer that binds to vascular endothelial growth factor was recently approved as a new treatment for age-related macular degeneration (1). In addition, efficient ribozymes for charging amino acid analogs onto a transfer RNA (tRNA) are available for incorporating amino acid analogs into proteins (2). As a result, RNA molecules have become useful biopolymers for biomedical research, diagnostics, and therapeutics.