Infectious DNA from coliphage T1

SummaryInfectious DNA from coliphage T1 was inactivated by 60Co-gamma-rays. The influence of inactivating species from water radiolysis in a medium of high protein contents was studied. The effect of increasing concentrations of protein on radiosensitivity and on the occurrence of DNA double-strand breaks (dsb) was tested. Contribution of dsb to the inactivating event increases with increasing concentration of protein in the medium. Under these conditions about 60 per cent of the DNA molecules contain dsb. Metal-chelating agents (EDTA) protect infectious DNA very efficiently. The possible site of action and some properties this chemical has in common with compounds of the cysteine-cysteamine group are discussed. From experiments with phage particles, it was concluded that the protein membrane is a barrier to many radical scavengers and inactivating species in the medium. Furthermore, the phage specific organization of DNA influences the radiation damage to the polynucleotide in many respects.