-globin mRNAs capped with m7G, m22.7G or m32.2.7G differ in intrinsic translation efficiency

Abstract

We examined the intramolecular effect of altered cap structures on translation efficiency of artificial β-globin mRNAs. For these studies, synthetic dinucleotides of the form X(5')ppp(5')G [X=7-methyl guanosine (m ⁷ G), 2, 7-dimethyl guanosine ( $m22.7G$ ) or 2,2,7-trimethyl guanosine ( $m32.2.7G$ ), were transcriptionally Incorporated into mRNAs, containing rabbit β-globin coding sequences, using T7 RNA potymerase and a β-globin cDNA template. These synthetic mRNAs were assayed in reticulocyte lysate for activity relative to m ⁷ G-capped mRNA. $m22.7G$ -Capped mRNA was found to be 1.5-fold more active than m ⁷ G-capped mRNA. Messenger RNA capped with $m32.2.7G$ was less active with activity of 0.24 relative to its m ⁷ G-capped counterpart (activity = 1.0). These data suggest that m ⁷ G-capped mRNAs become more active as translation templates after addition of a single N ² methyl moiety, which is especially pertinent to gene expression in togaviridae. The latter are observed to synthesize $m22.7G$ and $m32.2.7G$ -capped mRNAs in addition to m ⁷ G-capped templates during the course of infection in animal cells.