siRNA knockdown of huTRIM5α reduces VSV-G MLV-N restriction in HeLa/CD4 cells but has no effect on MLV-B and MLV-NB. (a) VSV-G pseudotyped MLV-N viral vectors were used to challenge HeLa/CD4 cells that were pre-treated with 50 pmol siRNA huTRIM5α, control siRNA and untreated cells. As expected, treatment with siRNA huTRIM5α resulted in a relief of the restriction of MLV-N cores, while treatment of cells with the control siRNA had no effect on the transduction. MLV-B viral vectors pseudotyped with restricted (MCN, MCR, RD114) and non restricted (VSV-G, Ampho and GALV) Envs were used to infect HeLa/CD4 cells that were pre-treated with the optimal siRNA huTRIM5α concentration determined for MLV-N (50 pmol), control siRNA or non-siRNA treated. Untreated NP2/CD4/CXCR4 cells were also infected as a control. The siRNA huTRIM5α treated cells showed no relief of restriction of the MLV-B viral vectors. (b) As for Figure 4a, but with MLV-NB virus. Data represent the average of three or more independent experiments +/- S.E.M.