Sedimentation characteristics and molecular weights of three poxvirus DNAs

Abstract

DNA from vaccinia, fowlpox, and juncopox viruses was released from virions by gentle treatment with detergents and 2-mercaptoethanol or pronase and sedimented through neutral and alkaline sucrose gradients. Using T4 DNA with a S 0,w 0 value of 61.4 as a standard, vaccinia DNA in neutral sucrose gradients had a S 0,w 0 value of 62.1, whereas the sedimentation coefficients of fowlpox and juncopox DNAs were 72.0 and 69.3, respectively. In alkaline sucrose gradients, all three poxvirus DNAs showed an increased sedimentation rate compatible with a single-stranded circular molecule or a linear molecule twice the length of the native double-stranded molecule. This increased sedimentation rate in alkaline sucrose indicates that, like vaccinia, the DNA from the two avian poxviruses does not separate into complementary strands upon denaturation, but appears to contain covalent links between the complementary strands, located at or near the ends of the native DNA molecule. The sedimentation data of the native poxvirus DNA molecules was converted into molecular weights using a variety of expressions for relating the two parameters. Vaccinia DNA was seen to have a molecular weight of 125 ± 2 × 10 6, whereas the fowlpox genome was 185 ± 5 x 10 6. DNA from juncopox appeared to be slightly smaller than the fowlpox genome. The two avian poxviruses contain almost 50% more DNA than vaccinia, and are among the largest viral genomes known.