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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...

RNA editing of the human parainfluenza virus type 3 (HPIV3) phosphoprotein (P) gene was found to occur for the accession of an alternate discontinuous cistron. Editing occurred within a purine-rich sequence (AAUUAAAAAAGGGGG) found at the mRNA nucleotides 791-805. This sequence resembles an HPIV3 consensus transcription termination sequence and is located at the 5'-end of the putative D protein coding sequences. Editing at an alternate site (AAUUGGAAAGGAAAGG), mRNA nucleotides 1121-1136, for accession of a conserved V cistron, which is present in a number of paramyxovirus P genes, was not found to occur in HPIV3. In contrast with many other paramyxoviruses, editing was indiscriminate with the insertion of 1-12 additional G residues not present in the gene template. RNA editing was found to occur in both in vivo (HPIV3 infected cells) and in vitro (purified nucleocapsid complexes) synthesized mRNAs. Further, the in vitro prepared mRNA was edited regardless of whether the nucleocapsid complexes were transcribed in the presence or absence of uninfected human lung carcinoma (HLC) cell lysates. These results support the notion that RNA editing appears to be exclusively a function of viral proteins.

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Clinical development of a mesogenic strain of Newcastle disease virus (NDV) as an oncolytic agent for cancer therapy has been hampered by its select agent status due to its pathogenicity in avian species. Using reverse genetics, we have generated a lead candidate oncolytic NDV based on the mesogenic NDV-73T strain that is no longer classified as a select agent for clinical development. This recombinant NDV has a modification at the fusion protein IMPORTANCEAvian paramyxovirus type 1, NDV, has been an attractive oncolytic agent for cancer virotherapy. However, this virus can cause epidemic disease in poultry, and concerns about the potential environmental and economic impact of an NDV outbreak have precluded its clinical development. Here we describe generation and characterization of a highly potent oncolytic NDV variant that is unlikely to cause Newcastle disease in its avian host, representing an essential step toward moving NDV forward as an oncolytic agent. Several attenuation mechanisms have been genetically engineered into the recombinant NDV that reduce chicken pathogenicity to a level that is acceptable worldwide without impacting viral production in cell culture. The selective tumor replication of this recombinant NDV, both in vitro and in vivo, along with efficient tumor cell killing makes it an attractive oncolytic virus candidate that may provide clinical benefit to patients.