Cell Transformation by Different Forms of Polyoma Virus DNA

Abstract

DNA extracted from purified polyoma virus contains closed and open molecules which are separable by velocity sedimentation either in the analytical or in the preparative ultracentrifuge. The closed configuration of the DNA gives rise to the fast band (component I) and the open configuration to a slow band, which is in some cases double (components II and III). Components I and II are able to produce plaques on mouse embryo monolayers, i.e., they possess cytocidal activity but which of the components cause cell transformation could not be determined owing to the lack of an adequate quantitative assay for transformation. A determination of the role of these DNA components in transformation is important, since it may clarify the mechanism of transformation. Such a determination is now made possible by the development of a sensitive quantitative assay for transformation caused by polyoma virus. This method is based on the ability of the transformed cells to form colonies in agar where the vast majority of the untransformed cells are unable to form colonies. Preliminary experiments have demonstrated that this method is also suitable for the study of the transforming ability of polyoma DNA.

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