Arenaviral genomes encode at least four proteins from two segments (Large and Small). The Large segment encodes a matrix protein (Z) and an RNA-dependent RNA polymerase (L); the Small segment encodes a nucleoprotein (NP) and the glycoprotein precursor GPC [2] . GPC is cleaved by a cellular protease to a stable signal peptide (SSP), and two subunits, GP1 and GP2. The three cleavage products form a stable complex and mediate virus attachment to host cells and fusion of the arenavirion envelope with that of the cell [10, 11, 12, 13, 14, 15] . GP1 mediates the binding of the virion to a cell-surface receptor, whereas the class I fusion protein GP2 mediates membrane fusion after internalization of the virion into an acidified endosome [16, 17] . Interrupting the interaction of GP1 with its cell-surface receptor is a current focus of antiviral development since it would prevent the first and pivotal step of arenavirus host-cell infection.