DNA STRAND BREAKAGE IS CORRELATED WITH UNALTERED BASE RELEASE AFTER GAMMA-IRRADIATION

Unaltered base release is correlated with strand breakage for gamma-ir radiated bacteriophage PM2 DNA in aqueous solution at pH 7.4. The yiel d of DNA strand breaks is determined by the agarose gel electrophoresi s method. High-performance liquid chromatography (HPLC) is used to ass ay the release of unaltered nucleic bases. Previously reported HPLC me thods have been updated. Unaltered base release is linear with dose up to 424 Gy, where up to 0.2% of all DNA bases are released. No detecta ble amounts of unaltered nucleosides are released and, besides unalter ed bases, only one other product released from DNA is observed. Base r elease yields do not reflect the PM2 GC content of 43%. Only 76% of al l prompt strand breaks appear to be associated with the release of an unaltered free base, whereby the guanine, cytosine, adenine and thymin e yields are 9, 27, 18 and 22% of the prompt strand break yield, respe ctively. Postirradiation incubation at 37 degrees C for 24 h increases the strand break yield 1.38-fold and the unaltered base release yield 1.76-fold such that 97% of the final strand breaks appear to be assoc iated with the release of an unaltered base, whereby the guanine, cyto sine, adenine and thymine yields are 10, 36, 23 and 28% of the final s trand break yield, respectively. These data indicate that, given prope r conditions, nearly every strand break leads to a base release. The b earing of these results on OH radical attack leading to strand breakag e and base release is discussed. (C) 1995 by Radiation Research Societ y