Energy requirements for damaging DNA molecules. II. Energy transfer from metastable states of excited gases to double-stranded phi chi 174 RF-DNA.

Abstract

SummaryThe double-stranded replicative form (RF) of DNA from bacteriophage ΦX174 was exposed to metastably-excited gases in extremely thin layers. The loss of plaque-forming ability and the frequency of single-strand breaks was measured in a spheroplast system and by centrifugation in neutral and alkaline sucrose gradients, respectively. The excitation energy of the various gases used amounts to 4·3 eV for H2*, 6·2 eV for N2*, 11·6 eV for Ar*, and 19·8 eV for He*. These energies are transferred to the RF-DNA molecules by ‘collisions of the second kind’. They are shown to produce identical effects on DNA. However, the actions of excited gases and that of Co γ-radiation on ΦX174 RF-DNA differ in many respects.(1) Single-strand breaks caused by excited gases do not measurably destroy the plaque-forming ability of the double-stranded ΦX174 RF-DNA; twenty (and possibly considerably more) single-strand breaks either do not interfere with the replication process, or are repaired with high efficiency in the host ...