Infectivity of Mo-MLV/GaLV p12 chimeras. The diagrams on the left show the design of chimeric Gag-Pol plasmids based on (A) Mo-MLV with either the whole of p12, or just the N-terminus or C-terminus of p12 replaced with the p12 from GaLV, and (B) GaLV with either the whole of p12, or just the N-terminus or C-terminus of p12 replaced with the p12 from Mo-MLV. These chimeric Gag-Pol plasmids were used to produce LacZ-encoding mutant VLPs in 293T cells and RT activity was quantified by a modified ELISA as a measure of viral synthesis (middle panels). Equivalent RT-units of VLPs were used to challenge D17 cells and infectivity was measured by detection of β–galactosidase activity in a chemiluminescent reporter assay (right panels). Results are plotted as the percentage of infectivity compared to the infectivity of the corresponding wild type VLPs for each species. The mean and range of three independent experiments are shown.