The transforming function of bovine papillomavirus DNA.

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Abstract
When bovine papillomavirus (BPV) or its 7.9-kilobase full viral DNA genome induces focal transformation of mouse cells, the viral DNA is maintained in the transformed cells as multiple episomal copies. This transforming capacity and maintenance of the episomal state previously were localized to a 69% subgenomic fragment of the viral DNA genome. To further characterize the BPV DNA sequences that encode the transforming function, a series of BPV DNA deletion mutants was created and the location of the deletions was correlated with the capacity of the deleted viral DNA to induce transformation of mouse cells. Two discontinuous segments of the viral DNA were required for transformation. One segment, near the 5'' end of the 69% transforming fragment, probably represents a control element of the viral DNA. The 2nd segment, which lies within the 3'' end of the 69% fragment, encodes transforming sequences of the viral DNA; ligation of a retroviral control element (the long terminal repeat DNA of Harvey murine sarcoma virus) to the 2.3-kilobase segment at the 3'' end of the 69% fragment induces transformation of mouse cells. In contrast to mouse cells transformed by the full-length BPV DNA genome, the cells transformed by the deleted BPV DNA genomes contained few viral DNA copies; at least some copies appeared to be integrated. Thus, different viral functions mediate cellular tranformation and maintain the viral DNA in its episomal state.