A major transcript of human papillomavirus type 16 in transformed NIH 3T3 cells contains polycistronic mRNA encoding E7, E5, and E1^E4 fusion gene

We have cloned cDNA of the major 1.8 kb mRNA from HPV 16-transformed NIH 3T3 cells (PM3T3). The entire nucleotide sequences of this cDNA were determined and compared with prototype HPV 16 genomic DNA sequences. The 5′-end of the cDNA was flanked by approximately 300 bp of cellular sequences, and the 3′-end of the cDNA sequences contained poly A residues following at nt 4230. HPV 16 sequences began at nt 124, downstream of a major viral p97 promoter, within the E6 open reading frame (ORF). The first splice donor site was at nt 226 and the splice acceptor site was at nt 409, suggesting that the E6 gene is inert. Second splice donor and acceptor sites were located at nt 880 and at nt 3357, respectively. This mRNA was thus shown to consist of three exons, resulting in polycistronic mRNA containing three potentially functional virus early genes-E7, E1^E4, and E5-actively transcribed in the transformant.