Recombinant DNA molecules comprising bovine papilloma virus type 1 DNA linked to plasmid DNA are maintained in a plasmidial state both in rodent fibroblasts and in bacterial cells.

Abstract

Transformed cells obtained after transfecting FR3T3 rat fibroblasts with DNA of bovine papilloma virus type 1 (BPV1) maintained only free copies of the viral genome. Transfection with BPV1 DNA inserted in a bacterial plasmid (pBR322 or pML2) did not produce transformants at a detectable rate, unless the viral sequences had been first excised from the plasmid. In contrast, transfer of the same plasmids by polyethylene glycol‐induced fusion of bacterial protoplasts with FR3T3 rat or C127 mouse cells led to significant transformation frequencies. A total of eight cell lines were studied, three rat and five mouse transformants, obtained with various BPV1 ‐ pML2 recombinants. In all cell lines, both BPV1 and plasmid sequences were maintained as non‐integrated molecules, predominantly as oligomeric forms of the transforming DNA. In the three rat transformants and in two of the mouse lines, parts of the non‐transforming viral region and some bacterial sequences were deleted. In the remaining three mouse lines, the monomeric repeat was a non‐rearranged plasmid molecule which could be re‐established as a plasmid in Escherichia coli after cleavage with “one‐cut” restriction endonucleases and circularization of the molecule.