The physical state and expression of the bovine papillomavirus type 1 (BPV-1) genome were analysed in two transplantable hamster sarcomas (HT and HT) after a low number of transplantations, in two tumourigenic cell lines derived from the first transplant of HT sarcoma and another transplantable sarcoma (HT) and in tumours obtained by grafting these cells. Blot hybridization experiments indicated the presence of multiple free copies of the whole viral genome in HT and HT tumour transplants (100 and 25 copies/cell respectively), irrespective of the number of or passages. In contrast, HT cells, and tumours induced by these cells, at early and late passages contained viral sequences probably integrated in the cell genome, in addition to the free viral DNA sequences. Polyadenylated viral transcripts were easily detected in HT, HT and HT tumours obtained at early passages and , with electrophoretic mobilities corresponding to 1200 to 1400 bases (HT, HT and HT), 1750 bases (HT) and 2500 bases (HT). Homologous sequences of the transcripts were localized in the transforming HI-dIII fragment of BPV-1 DNA, mainly in the HI-RI fragment (0.31 to 0.602 map units). In contrast, almost no viral transcription was detected in HT and HT cells after 50 subcultures and in the tumours induced by these cells. This suggests that the tumourigenicity of the HT and HT cells is compatible with a very low level of expression of the transforming region of the BPV-1 genome.


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