Abstract
Arenaviruses are rodent-borne agents of diseases, including potentially lethal human hemorrhagic fevers. These enveloped viruses encapsidate a bisegmented ambisense single-stranded RNA genome that can be packaged in variable copy number. Electron cryomicroscopy and image analysis of New World Pichinde and Tacaribe arenaviruses and Old World lymphocytic choriomeningitis virus revealed pleomorphic enveloped particles ranging in diameter from ∼400 to ∼2,000 Å. The surface spikes were spaced ∼100 Å apart and extended ∼90 Å from the maximum phospholipid headgroup density of the outer bilayer leaflet. Distinctive stalk and head regions extended radially ∼30 and ∼60 Å from the outer bilayer leaflet, respectively. Two interior layers of density apposed to the inner leaflet of the viral lipid bilayer were assigned as protein Z and nucleoprotein (NP) molecules on the basis of their appearance, spacing, and projected volume. Analysis of en face views of virions lacking the GP-C spikes showed reflections consistent with paracrystalline packing of the NP molecules in a lattice with edges of ∼57 and ∼74 Å. The structural proteins of retroviruses and arenaviruses assemble with similar radial density distributions, using common cellular components.
