FIG. 5.

Translation is sensitive to the presence of the N-7 methyl group on the inverted guanosine of the 5′ cap structure. (A) Schematic representation of mRNAs. The coding region of luciferase mRNA was followed by 114 nucleotides of vector (LUCX₁₁₄). Uniformly radiolabeled mRNAs were synthesized in vitro and differ, as depicted, only in the cap structure which they contain. (B) Translational stimulation of LUCX₁₁₄ mRNAs is influenced by the cap. mRNAs were injected into oocytes. Luciferase activity (arbitrary units, corrected for the amount of mRNA in each sample) is plotted against the time following injection. ▵, ApppG-capped mRNA; ◊, GpppG-capped mRNA; ⧫, m⁷GpppG-capped mRNA. (C) mRNAs varying in the 5′ cap structure are equally stable. mRNAs were analyzed by denaturing gel electrophoresis and autoradiography. Lanes 1 and 2, ApppG-capped mRNA; lanes 3 and 4, GpppG-capped mRNA; lanes 5 and 6, m⁷GpppG-capped mRNA. Samples were taken immediately following microinjection or after a 120-min incubation, as indicated.