A Novel methodology for characterizing strand-break termini and damaged bases in plasmid DNA exposed to ionizing radiations

Akamatsu, Ken; Wada, Seiichi*; Kobayashi, Yasuhiko

We have developed new methodology to characterize radiation damage in DNA. An enzyme system consisting of the 3' to 5'exonuclease snake venom phosphodiesterase (SVPD) and calf intestine alkaline phosphatase (CIAP) was used to examine the 3'termini of strand break sites. In this study, we hypothesized that the strand-break termini can be divided into two categories:CIAP-independent SVPD sites and CIAP-dependent SVPD sites. The former consists of strand-break termini that can directly be recognized and digested by SVPD without CIAP pretreatment, whereas the latter includes the termini that cannot be digested by SVPD without CIAP pretreatment. As the results, the G-value for total strand breaks in fully dried DNA irradiated with Co-rays was estimated to be 0.1 micromol/J. Moreover, the G-values of CIAP-dependent and CIAP-independent SVPD sites were estimated to be 0.078 and 0.024 micromol/J, respectively.