Artificial functional nucleic acids: Aptamers, ribozymes, and deoxyribozymes identified by in vitro selection

The discovery of natural RNA catalysts (ribozymes) inspired the use of in vitro selection methodology to develop artificial functional nucleic acids. In vitro selection is the experimental process by which large random-sequence pools of RNA or DNA are used as the starting point to identify particular nucleic acid sequences that have desired functions. When this function is binding of a molecular target, the functional nucleic acid is an RNA or DNA “aptamer”. When this function is catalysis of a chemical reaction, the functional nucleic acid is a “ribozyme” or “deoxyribozyme”; these are collectively termed “nucleic acid enzymes”. Since the first in vitro selection experiments in 1990, a wide variety of aptamers and nucleic acid enzymes have been identified. This chapter describes how aptamers, ribozymes, and deoxyribozymes are obtained by in vitro selection methodologies. Also addressed are the scope of the molecular targets that are bound and the chemical reactions that are catalyzed. Biochemical and structural characterizations of aptamers and nucleic acid enzymes are discussed. A final section introduces aptazyme, which are allosterically regulated nucleic acid enzymes.