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To generate infectious viral particles, viruses must specifically select their genomic RNA from milieu that contains a complex mixture of cellular or non-genomic viral RNAs. In this review, we focus on the role of viral encoded RNA structures in genome packaging. We first discuss how packaging signals are constructed from local and long-range base pairings within viral genomes, as well as inter-molecular interactions between viral and host RNAs. Then, how genome packaging is regulated by the biophysical properties of RNA. Finally, we examine the impact of RNA packaging signals on viral evolution.

Arenaviruses cause several viral hemorrhagic fevers endemic to Africa and South America. The respective causative agents are classified as biosafety level (BSL) 4 pathogens. Unlike for most other BSL4 agents, for the New World arenavirus Junín virus (JUNV) both a highly effective vaccination (Candid#1) and a post-exposure treatment, based on convalescent plasma transfer, are available. In particular, neutralizing antibodies (nAbs) represent a key protective determinant in JUNV infection, which is supported by the correlation between successful passive antibody therapy and the levels of nAbs administered. Unfortunately, comparable resources for the management of other closely related arenavirus infections are not available. Given the significant challenges inherent in studying BSL4 pathogens, our goal was to first assess the suitability of a JUNV transcription and replication-competent virus-like particle (trVLP) system for measuring virus neutralization under BSL1/2 conditions. Indeed, we could show that infection with JUNV trVLPs is glycoprotein (GP) dependent, that trVLP input has a direct correlation to reporter readout, and that these trVLPs can be neutralized by human serum with kinetics similar to those obtained using authentic virus. These properties make trVLPs suitable for use as a proxy for virus in neutralization assays. Using this platform we then evaluated the potential of JUNV nAbs to cross-neutralize entry mediated by GPs from other arenaviruses using JUNV (strain Romero)-based trVLPs bearing GPs either from other JUNV strains, other closely related New World arenaviruses (e.g. Tacaribe, Machupo, Sabiá), or the distantly related Lassa virus. While nAbs against the JUNV vaccine strain are also active against a range of other JUNV strains, they appear to have little or no capacity to neutralize other arenavirus species, suggesting that therapy with whole plasma directed against another species is unlikely to be successful and that the targeted development of cross-specific monoclonal antibody-based resources is likely needed. Such efforts will be supported by the availability of this BSL1/2 screening platform which provides a rapid and easy means to characterize the potency and reactivity of anti-arenavirus neutralizing antibodies against a range of arenavirus species. Fil: Leske, Anne. Friedrich Loeffler Institut; Alemania Fil: Waßmann, Irke. Friedrich Loeffler Institut; Alemania Fil: Schnepel, Kevin. Friedrich Loeffler Institut; Alemania Fil: Shifflett, Kyle. National Institutes of Health; Estados Unidos Fil: Holzerland, Julia. Friedrich Loeffler Institut; Alemania Fil: Bostedt, Linus. Friedrich Loeffler Institut; Alemania Fil: Bohn, Patrick. Friedrich Loeffler Institut; Alemania Fil: Mettenleiter, Thomas C.. Friedrich Loeffler Institut; Alemania Fil: Briggiler, Ana Maria. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud "Dr. C. G. Malbrán"; Argentina Fil: Brignone, Julia. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud "Dr. C. G. Malbrán"; Argentina Fil: Enria, Delia. Dirección Nacional de Instituto de Investigación. Administración Nacional de Laboratorio e Instituto de Salud "Dr. C. G. Malbrán"; Argentina Fil: Cordo, Sandra Myriam. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: Hoenen, Thomas. Friedrich Loeffler Institut; Alemania. National Institutes of Health; Estados Unidos Fil: Groseth, Allison. Friedrich Loeffler Institut; Alemania. National Institutes of Health; Estados Unidos