Photochemistry and structure in nucleic acids.

Research into the photochcmistry of biopolymcrs has increased in scope and scale to such an extent in recent years that it has become necessary to limit this review to a consideration of photochemical approaches to the structure of polynucleotides. Treatment proceeds from the constituent monomers to the polymer to emphasize the changes in photophysical and photochemical properties of the monomers when incorporated into the polymer. Studies of the mechanisms and structural requirements for the photoreactions in polynucleotides are complicated by low yields of reactions and the essential lack of luminescence from nucleotides in aqueous solution near room temperature. Contrariwise, the use of photochemical yields in an empirical way to indicate occurrence of conformational changes has been successful. The most successful use of photochemical reactions in polynucleotides has been for making specific structural modifications for structure --function studies.