Specificity for 3',5'-linked substrates in RNA-catalyzed RNA polymerization.

The finding that ribozymes can catalyze RNA chain elongation has led to the proposal that an early self-replicating system could have consisted of RNA alone. In such a chain elongation reaction, the Tetrahymena ribozyme was found to select 3',5'-linked substrates from a pool that contained a large molar excess of 2',5'-linked dinucleotides. The enzyme neither reacted with nor was inhibited by 2',5' phosphodiester linkages. The ability to exclude incorrectly linked substrates would have conferred an important selective advantage to a primordial RNA molecule with RNA replicase activity.