Rescue of silent integrated polyoma genomes suggests homologous recombination between resident and transfected DNA fragments.
Two defective polyoma virus genomes, deleted in the nucleotide sequences coding the N-termini of the tumor antigens, were introduced into Fisher 3T3 rat cells by DNA-mediated gene transfer (transfection). The resulting integrated genomes were incapable of conferring a transformed phenotype to the cells. However, after transfection of these lines with small polyoma fragments overlapping the deleted sequences, transformed clones were isolated. These clones were analyzed by Southern genomic blot hybridization and by isolation in E. coli of plasmids containing viral sequences excised following fusion with mouse polyoma growth-permissive cells. In all cases at least one intact copy of the early region of the polyoma genome was found. Furthermore, restriction sites adjacent to the initial inactive insertion remained unchanged in many of the transformed lines. These results show that functional restoration of the defective polyoma early region involves homologous recombination between the deleted viral genomes integrated in the cellular DNA and the transfecting viral fragments.
D000818:Animals; D000957:Antigens, Viral, Tumor / Q000235:genetics; D002459:Cell Fusion; D002460:Cell Line; D002472:Cell Transformation, Viral; D004261:DNA Replication; D004274:DNA, Recombinant; D004279:DNA, Viral; D005347:Fibroblasts; D005814:Genes, Viral; D051379:Mice; D009693:Nucleic Acid Hybridization; D011120:Polyomavirus / Q000235:genetics*; D051381:Rats; D011995:Recombination, Genetic; D014162:Transfection
D000957:Antigens, Viral, Tumor; D004274:DNA, Recombinant; D004279:DNA, Viral