UTR insertion/ deletion polymorphism does not significantly affect GJA5 mRNA stability or translational efficiency. (A) HL-1 murine cardiomyocytes transfected with vectors containing the firefly luciferase gene fused at its 3′ end to the GJA5 3′ UTR were measured for luciferase activity, normalized to the β-galactosidase activity of the transfection control vector. Shown are the mean activities, ± standard deviations. No significant differences in activity were observed for constructs carrying the deletion (Del, n=8), the insertion (Ins, n=4), or the insertion with a 3′ UTR point mutation (Ins + *22G>A, n=4) (P = 0.256, one-way ANOVA). (B) A GJA5 3′ UTR construct carrying the insertion was modified to include a mRNA instability sequence upstream of the GJA5 3′ UTR. The resulting positive control vector (ARE-Ins) demonstrated reduced luciferase activity compared to the unmodified vector (p<0.05, n=3).