An RNA-cleaving threose nucleic acid enzyme capable of single point mutation discrimination.

Threose nucleic acid has been considered a potential evolutionary progenitor of RNA because of its chemical simplicity, base pairing properties and capacity for higher-order functions such as folding and specific ligand binding. Here we report the in vitro selection of RNA-cleaving threose nucleic acid enzymes. One such enzyme, Tz1, catalyses a site-specific RNA-cleavage reaction with an observed pseudo first-order rate constant (kobs) of 0.016 min-1. The catalytic activity of Tz1 is maximal at 8 mM Mg2+ and remains relatively constant from pH 5.3 to 9.0. Tz1 preferentially cleaves a mutant epidermal growth factor receptor RNA substrate with a single point substitution, while leaving the wild-type intact. We demonstrate that Tz1 mediates selective gene silencing of the mutant epidermal growth factor receptor in eukaryotic cells. The identification of catalytic threose nucleic acids provides further experimental support for threose nucleic acid as an ancestral genetic and functional material. The demonstration of Tz1 mediating selective knockdown of intracellular RNA suggests that functional threose nucleic acids could be developed for future biomedical applications.