MT-RNR2 and influenza: While previous studies, including ours, showed both filamentous particles and irregular patches of glycoproteins on viral surfaces, including some patches of HN alone [1], the particles we observed here, in the absence of ultracentrifugation, were, in contrast, quite spherical and uniformly coated with a double layer of glycoproteins, comprised of HN and pre-fusion F. Ultracentrifugation can not only alter viral particle integrity, as has been shown for influenza, but also promote the artificial selection of viruses of a specific density or morphology [101].