Yields of Radiation-induced Main Chain Scission of Poly U in Aqueous Solution: Strand Break Formation Via Base Radicals

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Abstract
The G values [1.0 364 .cntdot. 10-7 mol material formed or destroyed per J energy absorbed] for single-strand breaks G(ssb) in polyuridylic acid (poly U) were measured by low-angle laser light scattering in aqueous solutions under various conditions (e.g. in the presence of N2O, Ar and tert-butanol). In N2O-saturated solutions at room temperature and pH 5.6, the G(ssb) is 2.3. The efficiency of ssb formation was found to be 41% for OH radicals, 19% for H atoms and .simeq. 0 for .**GRAPHIC**. On the basis of 20% and < 5% attack on the sugar moiety by OH radicals and H atoms, respectively, the large G(ssb) values obtained cannot be explained solely as resulting from radicals produced by reaction of OH radicals and H atoms on the sugar moiety. Base radicals produced by the reaction of OH radicals or H atoms with the uracil moiety can also lead to chain break formation in poly U via radical transfer to the sugar moiety.

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