Generation of a catalytic module on a self-folding RNA.

It is theoretically possible to obtain a catalytic site of an artificial ribozyme from a random sequence consisting of a limited numbers of nucleotides. However, this strategy has been inadequately explored. Here, we report an in vitro selection technique that exploits modular construction of a structurally constrained RNA to acquire a catalytic site for RNA ligation from a short random sequence. To practice the selection, a sequence of 30 nucleotides was located close to the putative reaction site in a derivative of a naturally occurring self-folding RNA whose crystal structure is known. RNAs whose activity depended on the starting three-dimensional structure were selected with 3'-5' ligation specificity, indicating that the strategy can be used to acquire a variety of catalytic sites and other functional RNA modules.