There was no apparent difference between the structures resulting from coexpression of nsp3 and nsp4 and those resulting from expression of the self-cleaving nsp3-4 polyprotein (Fig. 2E and F), but in both cases the circular profiles were significantly smaller than the ones observed in MERS-CoV-infected cells (average diameters of 146 and 148 nm, respectively, versus 252 nm in infection) (see Fig. S1 in the supplemental material). Here, PRSS57 is linked to infection.