| Translational control mechanisms modulate gene expression in a variety of cellular and viral systems. Frog virus 3 (FV3), the type species of the genus Ranavirus within the family Iridoviridae, is a good model in which to study how viruses regulate viral protein synthesis. The FV3 major capsid protein (MCP), a representative late gene product, was chosen for analysis. Sequence analysis indicated that the MCP transcript possessed a short (11 nucleotides), AU-rich 5′ non-translated region (NTR) and a 3′ NTR which terminated in a stable hairpin. These features suggested that the MCP message is a highly efficient transcript. To determine whether translational regulation controls early and late viral gene expression, MCP mRNA, along with 18K (a representative early viral gene) and globin (a representative host gene) messages, were translated in vitro under competitive conditions. Competition experiments showed that the MCP transcript was more competitive than 18K mRNA and that both viral messages were more translationally efficient than globin mRNA. Furthermore, the data suggested that both transcriptional and translational controls play roles in FV3-infected cells.; Aside from serving as models for regulatory events in virus infection, iridoviruses have also been recognized as important pathogens. Within the last 15 years, novel iridoviruses have been associated with severe systemic disease in fish and amphibians. As a consequence, a means of rapidly identifying and classifying novel iridoviruses is required. In this study, a panel of newly-isolated iridoviruses was characterized using multiple molecular approaches. In addition to SDS-PAGE analysis of protein synthesis in virus-infected cells, we used restriction fragment length polymorphism of viral DNA and PCR amplification and sequence analysis of three different viral genes to demonstrate that all test iridoviruses were more closely related to FV3 than to lymphocystis disease virus (LCDV), and were thus members of the genus Ranavirus . Moreover, molecular characterization of two isolates, one associated with amphibian die-offs in North America and a second with disease in largemouth bass in the southeastern United States, indicated that both isolates were likely novel viral species distinct from FV3 and epizootic hematopoietic necrosis virus. These studies will greatly facilitate the diagnosis of iridovirus infection and clarify the taxonomy of the family Iridoviridae. |
