A. Readthrough at the test stop signals UAGAAG, UGAAAG and UAAAAG in HEK293T cells with cognate or non-cognate suppressor tRNAs (UAG [black], UGA [grey] or UAA [white]) and tRNASer as a control (serine). The mean ± SEM for four replicates is shown. B. Effect of over-expressing cognate suppressor tRNAUGA, non-cognate tRNAUAG or control tRNASer on human antizyme +1 frameshift efficiency. The mean ± SEM for four replicates is shown. C. Effect on −1 frameshift efficiency of the HIV-1 element when UAG (black) or UGA (grey) suppressor tRNAs or the control tRNASer (white) are expressed. Frameshift efficiency was measured for the cognate, non-cognate, and control tRNAs. Note the change in scales between when the intercodon is the native GGG (left) and UGA or UGA with a complementary mutation restoring the stem (UGA_U, right). The mean ± SEM for four replicates (GGG) or six replicates (UGA and UGA_U) is shown. *P = < 0.05, **P = < 0.01, ***P = < 0.001.