The bovine papillomavirus distal "enhancer" is not cis essential for transformation or for plasmid maintenance

We constructed a mutant of bovine papillomavirus type 1 (BPV-1) DNA that lacked a transcriptional enhancer located 3' to the polyadenylation site of the early viral RNAs expressed in transformed cells. This mutant DNA, when separated from the procaryotic sequences, transforms mouse cells with an efficiency comparable to that of the full BPV-1 genome, and it exists as a stable multicopy plasmid in transformed cells. The BPV-1 distal enhancer suppresses the effects of a cis-inhibitory element in pML2 sequences but is not essential for the expression of the viral genes involved in cellular transformation or plasmid maintenance.