Evolution of a phosphorothioate RNA library during in vitro selection

We carried out an in vitro selection of aptamers from an RNA library with phosphorothioate linkages instead of normal phosphodiesters. This "thio-RNA" library had smaller dissociation rate constant (kd) to a target protein than a natural RNA library. On the basis of the results, an improved selection procedure to obtain ideal nucleic acid drugs will be discussed.