Host-cell reactivation of PHI X174 RF-DNA damaged by γ-ray-induced phenylalanine and water-radicals

SummaryAqueous solutions of the double-stranded form of ΦX174 DNA have been irradiated with γ-rays in the presence of phenylalanine. Evidence is presented showing that under these circumstances DNA inactivation is largely due to secondary amino acid radicals. Such reactions of organic radicals might play a role in living cells.If the irradiation is carried out under N2O, the apparent sensitivity of the DNA is markedly increased by testing its virus-producing capacity on spheroplasts prepared from Uvr− strains of Escherichia coli. Such a difference in survival on Uvr− and Uvr+ spheroplasts is not found in the presence of oxygen, nor does it occur after irradiation in the absence of the amino acid.Testing of irradiated DNA on spheroplasts of a Pol− strain results in a somewhat increased apparent radiosensitivity in the presence, but also in the absence of phenylalanine. This effect is not suppressed by irradiation under oxygen.