A novel small RNA virus isolated from the cotton bollworm, Helicoverpa armigera

A small RNA virus with novel characteristics has been isolated from laboratory-bred larvae of Helicoverpa armigera. Infection by the H. armigera stunt virus causes severe retardation of larval development and subsequent death. Its particles are isometric, 38 nm in diameter, and have a buoyant density of 1.296 g/ml in caesium chloride. The viral capsid has two major non-glycosylated protein components with M(r)s of 65 000 and 6000, and contains a genome composed of two non-polyadenylated single-stranded RNA molecules with lengths of 2.4 kb and 5.5 kb. The 5' termini of these RNAs are capped; their 3' termini are unblocked. In vitro translations of the viral RNAs showed synthesis of large proteins of sizes near the maximum coding capacity of each strand along with synthesis of numerous smaller proteins; no evidence for processing of precursors was seen. The physicochemical properties of the virus are most similar to those of the Nudaurelia omega virus, a provisional member of the Tetraviridae, although no antigenic relationship was observed between the two viruses. The bipartite genome and distinct capsid structure of these two viruses indicate the existence of a previously unrecognized virus group.