High dosage of TEF5 reduces UAA and UGA readthrough levels in the sup45-sl23tsmutant. The 33G-D373-rSL23 strain with the sup45-sl23tsmutation was transformed with one of the following plasmids: multicopy plasmids YEplac181-TEF5Δi (TEF5-Δi↑) or YEplac181 (M-empty), and centromeric plasmids pRS315-SUP45 (SUP45-CEN) or pRS315 (C-empty). The appropriate dual luciferase reporter plasmids were introduced into cells of obtained transformants. The transformants carrying plasmid pairs were grown in liquid C-Leu, Ura medium at 30°C and then readthrough levels were measured as described in Methods. The plasmid YEplac181-TEF5Δi causes a statistically significant decrease of UAA and UGA readthrough levels (P ≤ 0.02 and P ≤ 0.01, respectively) compared to those in transformants carrying YEplac181. Comparison of transformants bearing pRS315-SUP45 and pRS315 revealed statistically significant difference in readthrough of all stop codons: P ≤ 0.1, P ≤ 0.001 and P ≤ 0.05 for UAA, UGA and UAG codons, respectively.