FIG. 3.

HPV episomal copy number in S12 cells transfected with HPV-16 E2. S12 cells were transfected with HPV-16 E2-expressing plasmid or vector alone and cultured for 3 days posttransfection. Total DNA was extracted, and 10 μg/sample was analyzed by agarose gel electrophoresis and Southern blotting. Hybridization was carried out using ³²P-labeled HPV-16 L1 (capsid protein gene) DNA as the probe. Upon extensive passage, S12 cells lose the episomal copies of the HPV genome, though integrated copies remain. Lane 1, high-passage (≈50) S12 cells. Lane 2, low-passage (≈15) S12 cells as used in our experiments. Lanes 3 and 4, S12 cells transfected with empty vector DNA (lane 3) or with HPV-16 E2 DNA (lane 4).