CPSF4 and infection: Although we apparently only detect a small proportion of ‘helix-open’ NS1 in the cytoplasm relative to nucleus at 8 h post-infection, this may be explained by the fact that NS1-mediated activation of PI3K is a catalytic process, thus requiring few NS1 molecules, whereas CPSF30 inhibition requires stoichiometric sequestration by many NS1 molecules.