Expression of the HPV-L1 transcript over time by RT-PCR. After infecting Vero cells with the FPL1 recombinant, in duplicate, the expression of the transgene was evaluated every 3 days. The expression levels, as determined by densitometric analysis, extended up to day 21 p.i. (530 bp). The data are expressed as means (±standard deviation). Amplification of β-actin RNA (518 bp) is also shown. Mock-infected cells were always negative, as were cells infected with FPwt or amplified in the absence of AMV-RT (data not shown).