Figure 1. Lassa virus structure showing the organization of the surface glycoproteins GP1 and GP2, the nucleoprotein NP, the L and Z proteins. Also shown are the L and S RNA segments, which actually exist in circular complexes with large amounts of NP and small numbers of molecules of L protein.

Figure 2. The ambisense genome organization, replication strategy and mechanism of protein synthesis is illustrated for the S RNA of Lassa viruses. The nucleoprotein (NP) gene is encoded in the viral complementary sense at the 3¢-end of viral genome. The glycoprotein precursor (GPC) gene is encoded at the 5¢-end of the genome in the viral sense. Synthesis of NP mRNA occurs directly from the genome template, whereas synthesis of GPC mRNA requires viral replication to produce an intermediary viral complementary antigenome RNA. The GPC is subsequently cleaved to produce GP1 and GP2 proteins. A similar RNA synthesis phenomenon occurs with the L RNA to produce both L mRNA and Z mRNA.