TRIM5α is the main mediator of the IFN-induced N-MLV restriction. A. HeLa and Vero cells were transfected with a siRNA targeting luciferase (Luc) or TRIM5α (siRNA H1, HA2 or A3), as indicated, and stimulated 24 h later with 1000 U/ml of IFN-β for 8 h. Total RNA was extracted and the levels of TRIM5α mRNA were determined by quantitative RT-PCR and normalized to GAPDH. The mean ± SD of duplicates is shown. B. HeLa or Vero cells were transfected with siRNA targeting luciferase (Luc), TRIM5αhu (H1 or HA2) or TRIM5αagm (HA2 or A3), as indicated. The next day, cells were stimulated with 1000 U/ml of IFN-β for 8 h and challenged with a GFP-expressing N-MLV vector. The percentage of GFP-positive cells was determined by FACS 48 h post-transduction. Data are from a typical experiment representative of three independent experiments.