Sequence-selective scission of RNA has been attracting interests of chemists and biochemists, since it is essential for molecular biology and therapy. If only one RNA can be chosen from many other RNAs and selectively cleaved at the desired site, it opens the way to new RNA science (regulation of expression of a specific gene in cells, advanced therapy, RNA manipulation, and others). However, none of the naturally occurring ribonucleases shows such a high sequence-selectivity. This is why sequence-selective artificial ribonucleases are desirable.