Pathways of DNA repair in T4 phage: II. Sedimentation analysis of intracellular DNA in repair-defective mutants

The function of various pathways of repair was assessed by sucrose gradient centrifugation of uv-irradiated intracellular T4 DNA. Mutation in the v gene inhibits the excision repair pathway and results in a slower endonucleolytic reaction, a delay in “joining” of fragments and a decreased rate of DNA replication following uv irradiation. Mutations in the x or y genes inhibit an alternate pathway and result in the failure to “join” single-strand breaks after irradiation. In the absence of uv irradiation, the x and y mutations lead to the accumulation of DNA with single-strand breaks and a decrease in the amount of concatemers. We postulate that the x and y genes are involved in a “joining” reaction involving DNA fragments.