Duplication of a viral enhancer sequence improves the stability of a vector based on BPV-1 DNA.

Various recombinant constructions involving bovine papillomavirus type 1 (BPV-1) DNA and bacterial plasmids have been tested for their ability to transform mouse C127 cells and replicate as intact extrachromosomal monomeric structures. When BPV-1 DNA was linked to pBR328, pAT153 or derivatives of these plasmids lacking the 344 bp HindIII-BamHI fragment or another small segment, the resulting vectors replicated in C127 cells as high molecular weight structures and, in some cases, deleted extrachromosomal forms. The sequences which became deleted were generally the non-BPV-1 sequences. Duplication of the 3' distal enhancer sequence of BPV-1 DNA in one of the vectors increased its stability upon introduction into C127 cells, but some deleted and high molecular weight forms were still observed.