Flaviviruses have imperfect icosahedral symmetry

Significance Icosahedral symmetry has generally been assumed during cryo-electron microscopy reconstructions of most spherical viruses, including flaviviruses. However, unlike other viruses, the flavivirus core appeared to lack an ordered structure. By removing symmetry constraints, it was found that in immature flaviviruses, the nucleocapsid core is asymmetrically positioned with respect to the lipid membrane and glycoprotein shell. Thus, the assembly and budding process leads to imperfect icosahedral symmetry, which may affect virus maturation. Similarly, in the study of many other viruses, icosahedral averaging may have hidden biologically significant events.