The Release of Thymine Base Damage from the DNA of γ-Irradiated Tetrahymena pyriformis

The release of ..gamma..-irradiation-induced thymine base damage of the 6-(hydroxy or hydroperoxy)-5,6-dihydrothymine type (t') from the DNA of Tetrahymena pyriformis has been determined during various postirradiation conditions. After 40 krad, t' is released from 30 min to 3 hr. Postirradiation hypoxia inhibits release. The antibiotics actinomycin D and cycloheximide prevent some or all of the t' release if added sufficiently early. The data suggest an actinomycin D-sensitive event necessary for t' release which is completed some 40 min before the completion of a requisite cycloheximide-sensitive event that in turn precedes the actual release of t' by another 40 min. An enzymatic activity which preferentially degrades irradiated DNA and releases t' has been detected in the postmitochondrial supernate from recently irradiated Tetrahymena.