Sequencing studies of pichinde arenavirus S RNA indicate a novel coding strategy, an ambisense viral S RNA

Abstract

Analyses of the complete sequence of the 1.1 x 106-dalton, small (S) RNA of the arenavirus Pichinde and virus-induced cellular RNA species have revealed that the viral nucleoprotein, N,' is coded in a subgenomic, non-polyadenylated, virus-complementary mRNA corresponding to the 3' half of the viral RNA (Auperin et al., Virology 134:208-219, 1984). By contrast, a second S-coded product, presumably the viral glycoprotein precursor (GPC), is coded in a subgenomic, virus-sense mRNA corresponding to the 5' half of the RNA. Between the two genes is a unique RNA sequence that can be arranged in a hairpin configuration and may function as a transcription terminator for both genes. The term ambisense RNA is coined to describe this novel coding strategy of a viral RNA. The unique feature of the strategy is that the presumptive GPC mRNA and its translation product cannot be made until viral RNA replication has commenced. In addition, it allows the two subgenomic mRNA species to be regulated independently from each other or from other viral mRNA species. The implications of this strategy on possible mechanisms for the induction and maintenance of viral persistence, an important attribute of arenavirus infections, are discussed. Arenaviruses are enveloped RNA viruses that have a genome consisting of two species of RNA, designated on the basis of size differences as large, L (ca. 2.5 x 106 daltons) and small, S (1.1 x 106 daltons) (vide infra) (19, 20). The viruses in the Arenaviridae family include four human pathogens that are responsible for aseptic lymphocytic choriomeningitis (LCM virus), Argentine hemorrhagic fever (junin virus), Bolivian hemmorrhagic fever (Machupo virus), and Lassa fever (Lassa virus) (20). These, and the nine other viruses in the family, commonly infect rodents (or fruiteating bats for Tacaribe virus), typically involving persistent, lifelong infections in those hosts (20). Persistent infections are also readily established in vitro and are characterized by an abundance of nucleoprotein and a paucity of glycoprotein or infectious virus (14, 20). These properties, plus that of including ribosomes within virus particles (10), set arenaviruses apart from all other RNA viruses. Genetic and molecular studies (13, 23) have established that the arenavirus S RNA codes for the major structural nucleoprotein, N, and the two glycoproteins, Gl and G2, that are derived from an intracellular precursor protein, GPC (8). The L RNA codes for a large protein that is believed to be a transcriptase-replicase component (13). The transcriptional strategies of the two viral RNA species of arenaviruses are unknown. If the viruses are similar to the negativestranded rhabdoviruses or paramyxoviruses, then individual virus-complementary (vc) mRNA species may be synthesized from the S RNA to serve as templates for the two Scoded proteins (7). Alternatively, a polycistronic mRNA may be transcribed coding for a polyprotein that, through proteolytic cleavage, yields the desired products. Based on the transcriptional strategies of o...

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