Short lifetime structures appearing in RNA and DNA.

The structure and function of unstable single-stranded DNA (ssDNA) have not been widely examined. While numerous studies have investigated DNA as an information molecule, the different potentials of DNA, particularly those of ssDNA, remain unclear. For polypeptides, the significance of denatured structures has been established in the past two decades. Polynucleotides have chemically distinct properties from polypeptides, but their behaviours have not been thoroughly studied. In this review, three different phenomena related to unstable ssDNA are discussed: i) ssDNA cleavage of restriction enzymes; ii) single-stranded conformation polymorphism, which can be theoretically explained by single-stranded conformation dynamics; and iii) random PCR (Polymerase Chain Reaction). These features can be utilized for scientific or technical applications. Previous studies showed that the phenomena exhibited by ssDNA were correctly understood only when unstable and transient structures were taken into account. Transient structures of ssDNA may have undiscovered functions governed by very rapid processes and/or multi-diversity states because of their intrinsic natures.