English: Arenavirus virion structure and genome organization. (A) Electron microscopic image of Lassa virus (LASV) illustrates the common virion architecture of arenaviruses. Bar, 100nm. (B) Schematic representation of arenavirus virions. The viral envelope, a lipid bilayer derived from the host cell plasma membrane, contains multiple copies of glycoprotein spikes on the surface that are required for receptor binding and virus entry. The Z protein forms a matrix layer underneath the viral membrane. The nucleoprotein NP associates with the polymerase L to form together with the genomic RNA the ribonucleoprotein (RNP) complex. (C) Genome organization of arenaviruses. Arenaviruses contain a bi-segmented negative-strand RNA genome, composed of the small (S) RNA segment and the large (L) RNA segment. Each RNA segment encodes two viral proteins in an ambisense orientation. The open reading frames are separated by intergenic regions.