Catalytic DNAzymes: Derivations and functions

Background: Although catalytic RNA enzymes (CRzs) are naturally occurring in many organisms, their DNA counterparts (CDzs) were developed by in vitro selection/evolution from random sequence libraries. Objective: To provide a brief overview of how CDzs have been selected in vitro, and of their properties and functions, as well as their possible future utility. Methods: We concentrated on examples of 'direct' selection of CDzs. Many CDzs have been used in biological settings, for example downregulation of target mRNAs, while many more recent applications use CDzs in biosensor and nanotechnology settings. Conclusions: Although much work has concentrated on using CDzs for regulating gene expression, their potential as nucleic acid medicines has diminished substantially, supplanted by simple antisense oligonucleotides and, more recently, by small interfering RNAs (siRNAs). It seems unlikely that CDzs will have clinical utility. In contrast, they are likely to have significant potential in the sensor/nanotechnology arena.