Organization of Polyoma Virus DNA in Mammary Tumours of Athymic Mice

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Abstract
Restriction mapping of polyoma virus DNA in mammary tumors of athymic mice gave patterns that varied with the tumor examined. These reflected differences in both the organization and the state of integration of virus genomes in the host chromosomes. All tumors contained tandemly integrated full-length and defective virus genomes. Some tumors also contained unintegrated virus DNA molecules, some full-length and others defective. The deletions were localized in the virus genomic sequences coding for the distal part of the large T antigen. After the first transplantation, the organization of polyoma virus genomes in tumors remained essentially unchanged through 4 successive transplantations. The tumor cells that initially contained free virus DNA molecules continued to possess such molecules during serial transplantations. The virus DNA molecules in transplanted tumors lacking unintegrated virus genomes were more methylated than in tumors containing unintegrated virus genomes.