Abstract
Examination of the physical structure of cauliflower mosaic virus DNA by electron microscopy and ultracentrifugal analysis showed that the DNA could be isolated mainly as a circular molecule of mol. wt. 4.7 x 106. Nearest-neighbour frequency analysis showed that the DNA has a chemical structure which exhibits close similarities to that of the host cauliflower DNA. The relationships of this plant virus DNA and the small mammalian virus DNAs to the DNA of their respective hosts are discussed.