Mechanism of phage inactivation by radiation

Abstract Bacteriophage show two completely different types of response to radiation depending on whether they are irradiated in dilute aqueous solution, where the major lethal event is due to external radicals formed in the water, or whether they are irradiated in nutrient broth or some other radical scavenging medium; under these protected conditions a major lethal event is double strand breaks in the DNA. Single strand breaks do not appear to matter but the contribution of base damage has not yet been directly measured. In dilute solution the most effective radical for phage inactivation is the hydrogen atom followed by the OH radical and the hydrated electron, in that order. The mechanism of inactivation appears to be a radical attack on the phage tail causing a premature release of the DNA from the phage head. It is suggested that the energy for DNA release is stored in the tail and that the hydrogen atom triggers the release of this energy.