Yields of radiation-induced main chain scission of poly U in aqueous solution: strand break formation via base radicals.

The G values for single-strand breaks G(ssb) in polyuridylic acid (poly U) have been measured by low-angle laser light scattering in aqueous solutions under various conditions (e.g. in the presence of N2O, Ar and t-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 per cent for OH radicals, 19 per cent for H atoms and congruent to zero for e-aq. On the basis of 20 per cent and less than 5 per cent 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. It is therefore proposed that 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.