Bleomycin mediated degradation of DNA-RNA hybrids does not involve C–1′ chemistry

Incubation of Fe(ll) bleomycin and O2 with a number of ′A′-like DNA-RNA hybrid homopolymers at 4 atm O2 results in formation of base propenal and base In a ratio of approximately 1.0:1.0. This ratio differs dramatically from the corresponding ratio of approximately 10:1.0 observed when activated BLM degrades ′B′-like DNA homopolymers. Experiments were undertaken to detemine if the shift to enhanced base production observed in the A-like hybrids is the result of C-1′ chemistry in addition to the C-4′ chemistry normally observed with B-like DNA under identical conditions. Increased accessibility of the 1′-hydrogen might be anticipated due to widening of the minor groove in the A-like conformers. Experiments using poly([1′-3H]dA) poly(rU) and poly([U-14C]dA) poly(rU indicated that neither 3H2O nor deoxyribonolactone accompanied adenlne release. In addition, studies using poly([4′-2H]dA) poly(rU) and poly([1′-2H]dA) poly(rU) unambiguously establish that the altered base to base propenal ratio is not the result of C–1′chemistry, but a direct consequence of C–4′ chemistry.