Furuichi, working in Shatkin's laboratory, discovered that the viral mRNAs synthesized in vitro by the virion-associated RNA polymerase of reovirus contain a unique 5′-terminal structure m7GpppNm or cap. The precise biosynthetic pathways leading to the cap formation were then elucidated. These and other breakthroughs eventually led to the finding that this unique cap structure is also present in both the eukaryotic cytoplasmic mRNAs and heterogeneous nuclear RNAs, which in turn led to the discovery of mRNA splicing, critical to mRNA vaccines. With M. Morgan and S. Muthukrishnan.
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