Isolation of the complementary strands of vaccinia virus DNA

Separation of the complementary strands of vaccinia virus DNA by density centrifugation was attempted. Only non-cross-linked DNA molecules were used in these experiments. The best results were obtained using centrifugation in alkaline Cs₂SO₄ density gradients after denaturation of the DNA, followed by recycling of the isolated strands. Under these conditions, the heavy strand banded at a density of 1.480 g/cm³ and the light strand at 1.465 g/cm³. Incubation of denatured vaccinia DNA with ribopolymers, followed by centrifugation in CsCl density gradients, did not result in strand separation. Annealing experiments indicated that the strands isolated by alkaline Cs₂SO₄ density gradients were complementary.