Extra copies of TEF3 , but not of TEF4 reduce efficiency of UAA readthrough in the sup45-sl23tsmutant. The 33G-D373-rSL23 strain was transformed with one of the multicopy plasmids YEplac181-TEF2 (TEF2↑), YEplac181-TEF3 (TEF3↑), YEplac181-TEF4Δi (TEF4-Δi↑), YEplac181-TEF5Δi (TEF5-Δi↑), YEplac181 (M-empty) or centromeric plasmids pRS315-SUP45 (SUP45-CEN) or pRS315 (C-empty). The appropriate dual luciferase reporter plasmids were then introduced into cells of obtained transformants. The transformants with plasmid pairs were grown and readthrough measured as described in legend to Figure 3 and in Methods. The plasmids YEplac181-TEF3, YEplac181-TEF5Δi and pRS315-SUP45 cause a statistically significant (P ≤ 0.02, P ≤ 0.002 and P ≤ 0.01, respectively) decrease of UAA readthrough levels compared to those in transformants carrying corresponding empty vectors. The levels of UAA readthrough are increased in transformants with YEplac181-TEF2 as compared with that in transformants with YEplac181 (P ≤ 0.01).