Ultraviolet-induced 8,8-adenine dehydrodimers in oligo- and polynucleotides.

Characteristic fluorescence excitation and emission is induced by either acetone-sensitized 313 nm irradiation of mixtures of 8-bromoadenosine and adenosine or 254 nm irradiation of oligo- and polynucleotides containing adenine neighbors. The acetone-sensitized reaction involves cleavage of bromine from 8-bromoadenosine with activation of C-8, leading to formation of an 8,8-adenosine dehydrodimer. Comparable fluorescence properties arise in the unsensitized photoreaction of dApdA, pdApdA, ApA, poly(dA), poly(A), poly(dA.dT), and poly(dA.U). The previously unidentified adenine ultraviolet photoproduct described by Porschke has been isolated as several variants from solutions of pdApdA and poly(dA) irradiated at 254 nm. Based upon fluorescence spectra and mass spectra, these variants are shown to contain the 8,8-adenine dehydrodimer moiety.