A repair of single-strand DNA breaks has been detected in irradiated adenovirus following the infection of human cells. Adenovirus type 2 was given graded doses of cobalt-60 gamma rays at -75°C and subsequently used to infect human KB cells at approximately 100 PFU (original)/cell. The viral DNA was then assayed for single-strand breakage on alkaline sucrose gradients before, and at various times after, infection. The number of DNA molecules with no single-strand breaks increased after infection reaching a maximum fraction of whole molecules about 25 hr after infection. The rate of increase in the fraction of whole DNA molecules was enhanced at a lower input multiplicity of 25 PFU/cell and reduced at a higher input multiplicity of 250 PFU/cell. The maximum fraction of whole molecules obtained after infection coincides with the survival of the plaque forming ability of the virus and suggests that the repair of single-strand breaks leads to restoration of the biological expression of the viral DNA.

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