Figure 4

Response to exogenous c-Myb expression of FeLV LTRs containing variable numbers of the 21-bp element. Recombinant FeLV LTRs were constructed that contained 1, 2 or 3 copies of the 21-bp element and were cloned into a firefly luciferase reporter plasmid. LTR reporter plasmids or a 5X MRE positive control plasmid (500 ng) were introduced by lipid-mediated transfection in triplicate into feline embryonic fibroblasts (FEA) together with the Renilla luciferase reporter plasmid pRL-SV40 (5 ng) and a c-Myb expression plasmid in increasing concentrations (0 – 500 ng). Cell lysates were harvested 24 hours later and luciferase activity was quantified. Data are reported as a ratio of firefly to Renilla luciferase activity. Shown are data from a representative experiment repeated three times independently.