Ultraviolet irradiation of nucleic acids: formation, purification, and solution conformational analyses of the cis-syn and trans-syn photodimers of UpU.

Uridylyl(3'-5')uridine (UpU) is subjected to aqueous acetone photosensitized radiation with sunlamps. These irradiation conditions form only cyclobutane-type photodimers. Purification of a specific configurational photodimer is accomplished by using C-18 reverse-phase high-performance liquid chromatography. Multinuclear NMR analysis is used to analyze photoproduct formation and to determine conformational features of these photodimers. Four photodimers are identified, with the cis-syn isomer predominant. The cis-syn and trans-syn photodimers of UpU exhibit markedly different furanose and exocyclic bond conformations. A comparison of the properties of the cis-syn dimers of UpU with those of dTpdT reveal many similar conformational features but also some that are different.