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The reason why the influenza virus mRNA is stable and possesses nuclear export and translation capabilities is that it acquires the 5′ cap (1) structure during a process called cap snatching. During the cap snatching process, the virus-dependent RNA polymerase (FluPol) binds to the host RNA polymerase II (Pol II) and the newly emerging transcript. Subsequently, the FluPol endonuclease cuts out a capped RNA fragment, which serves as a primer for viral gene transcription. Here, we present the low-temperature electron microscopy structure of FluPol, combined with the elongation factor DSIF in a complex with the elongation-type Pol II in a pre-cutting state. This structure indicates that FluPol directly interacts with Pol II and DSIF, positioning the FluPol endonuclease domain near the RNA exit channel of Pol II. These interactions are crucial for the endonuclease activity of FluPol and its activity in the cell. The second structure was captured after cap snatching, showing that the cut capped RNA rearranges within FluPol and directs the 3′ end of the capped RNA towards the FluPol polymerase active site for viral transcription initiation. Our research results collectively reveal the molecular mechanism of the co-transcriptional cap of FluPol. This research was published in Nature under the title "Mechanism of co-transcriptional cap snatching by influenza polymerase".
Reference News:
DOI: 10.1038/s41586-026-10189-0
