Natural occurrence of cross-linked vaccinia virus deoxyribonucleic acid

The molecular weight of native vaccinia deoxyribonucleic acid (DNA) is 1 to 1.17 times that of native T4 DNA. Sedimentation of denatured vaccinia DNA through alkaline sucrose gradients yields an apparent molecular weight greater than twice that of denatured T4 DNA, implying that the complementary strands of vaccinia DNA do not separate upon denaturation. When alkali-denatured vaccinia DNA is neutralized, it has the physical chemical properties of native DNA when tested by sedimentation through neutral sucrose gradients, banding in CsCl, and by hydroxylapatite chromatography. We conclude that almost all mature vaccinia DNA molecules contain a small number of naturally occurring cross-links.