STRUCTURAL EVOLUTION OF THE DNA OF PSEUDORABIES-DEFECTIVE VIRAL PARTICLES

The structure of the DNA in two independently derived populations of pseudorabies-defective virions at different levels of passage at high multiplicity was analyzed by the use of restriction endonucleases and by the Southern blot technique. At relatively early stages of their evolution, the DNA of both populations of defective virions were enriched similarly for sequences originating from the middle and from the end of the long unique region of the viral genome. In both cases a recombinational event had occurred between these regions of the viral genome leading to the formations of a segment of DNA that subsequently became amplified. At later passages the composition of the DNA in the two populations of defective virions differed: in one population, Pr(1), significant differences in the DNA composition were not detectable between early and late passages; in the other, Pr(2), a large segment of DNA became reiterated in which one of the inverted repeats and part of the short unique region were linked to segments of DNA originating from the middle and from the end of the long unique region. Even after their DNAs had diverged considerably, the two populations of defective virions retained some features in common. The presence of these common features might account possibly for the similarities in the biological properties of the two defective virion populations. © 1979.