Alkali-labile sites and post-irradiation effects in gamma-irradiated biologically active double-stranded DNA in aqueous solution.

Gamma-irradiation of double-stranded RF-DNA of bacteriophage phi X174 in aqueous solution in the presence of oxygen produces at least one type of alkali-labile site. It is lethal and gives rise to breaks by alkali and is identical with the damage which becomes manifest by post-irradiation heat treatment. The effect of alkali is dependent on temperature. Furthermore, the excision repair system is not involved in eliminating lethal nucleotide damage in RFI-DNA.