Biophysical Properties and Thermal Stability of Oligonucleotides of RNA Containing 7,8-Dihydro-8-hydroxyadenosine

Circular dichroism (CD) was used to assess the stabiliza-tion/destabilization imposed by oxidative lesion 7,8-dihy-dro-8-hydroxyadenosine (8-oxoA) on strands of RNA with different structural motifs. RNA:RNA homoduplex destabilization was observed in a position dependent manner using 10-mers as models that displayed differen-ces between 12.7 and 15.1C. We found that increasing the number of modifications resulted in depressed Tm val-ues of about 12–15C per lesion. The same effect was observed on RNA:DNA heteroduplex samples. We also tested the effects of this lesion in short hairpins containing the tetraloop UUCX (X5A, 8-oxoA). We found that the stem was hypersensitive to substitution of A by 8-oxoA and that it destabilized the structure by>23C. Concom-itant substitution at the stem and loop prevented forma-tion of this secondary structure or lead to other less-stable hairpins. Incorporation of this lesion at the first base of the loop had no effect on either structure. Overall, we found that the effects of 8-oxoA on RNA structure are position dependent and that its stabilization may vary from sharp decreases to small increments, in some cases, leading to the formation of other more/less stable struc-tures. These structural changes may have larger biological implications, particularly if the oxidatively modified RNA persists, thus leading to changes in RNA reactivit