Alternative 5′ UTR isoforms differ in translation efficiency in vitro. (A) The longest and shortest 5′ UTR variants for nine genes with heterogeneous 5′ UTRs. (B) Schematic of reporter constructs and translation assay. (C) Representative ethidium bromide stained gels used to normalize luciferase activity to mRNA concentrations. (D) Mean normalized luciferase activity from translation of capped (5′-m7GpppG) mRNAs. Error bars represent standard deviations. P-values determined by Student's t-test (two-tailed) are indicated above the bars; (*) P < 0.05; (**) P < 0.01; (***) P < 0.001. (E) Comparison of mean translation activity to (left) 5′ UTR length and (right) predicted stability as determined by free-energy minimization using mfold (Zuker 2003).
