Bovine papillomavirus contains multiple transforming genes

Abstract

Bovine papillomavirus type 1 (BPV-1) and its cloned full-length DNA can transform rodent cells in vitro, and the viral DNA persists as an extrachromosomal multicopy plasmid in these transformed cells. Previous studies have identified at least five discrete viral RNAs that are expressed in BPV-1 transformed cells and have shown that these transcripts share a 3' coterminus. To further define the structure of these RNAs and to characterize the functions of individual viral transcripts, we constructed a cDNA library with mRNA from BPV-1-transformed mouse C127 cells using an Okayama and Berg plasmid. From a library of 10(5) independent clones, 200 BPV-1 specific clones were isolated and characterized. Sequence analysis has revealed differential splicing patterns for the mRNA species in BPV-1 transformed cells. In conjunction with the open reading frames (ORFs) deduced from the BPV-1 DNA sequence, it is possible to predict the structure of the potential encoded proteins. The vector used to generate these cDNA clones contains mammalian cell transcriptional regulatory elements, facilitating their functional characterization. We have identified two distinct classes of cDNA clones that can each independently transform mouse C127 cells. One class of cDNA clones contains the E2 ORF intact and the second contains the E6 ORF intact. These two putative viral functions appear to act synergistically in transforming mouse C127 cells in vitro.