Insect BTI-TN-5B1-4 (Tn5) cells have been used extensively with recombinant baculoviruses to express foreign genes. When a recombinant baculovirus containing the hepatitis E virus capsid protein gene was used to infect Tn5 cells, unknown virus particles in addition to the anticipated hepatitis E virus-like particles were produced in the infected cells. The unknown virus particles were 35 nm in diameter and contained RNA that was highly homologous to full-length RNA1 (3,107 bp) and RNA2 (1,383 bp) genomic RNAs of flock house virus. Surprisingly, both RNAs seen in these induced nodavirus particles could be amplified from commercially available Tn5 cells without infection with or induction by a baculovirus. The nucleotide sequences from the purified nodavirus particles and the normal Tn5 cells were identical, demonstrating that the Tn5 cells themselves were latently infected with a nodavirus. However, the generation of nodavirus particles was significantly stimulated by infection with recombinant baculoviruses. Phylogenetic analysis suggested that this new nodavirus belongs to the genus Alphanodavirus in the family Nodaviridae.
Numerous small, RNA-containing insect viruses are currently classified as picornaviruses, or as 'picorna-like', since they superficially resemble the true picornaviruses. Considerable evidence now suggests that several of these viruses are members of a distinct family. We have determined the gene sequence of the capsid proteins and the 2.4 A resolution crystal structure of the cricket paralysis virus. While the genome sequence indicates that the insect picorna-like viruses represent a distinct lineage compared to true picornaviruses, the capsid structure demonstrates that the two groups are related. These viral genomes are, thus, best viewed as composed of exchangeable modules that have recombined.
An insect virus, called Manawatu virus (MwV), was isolated from a larva of the New Zealand grass grub Costelytra zealandica (White) (Coleoptera: Scarabaeidae). MwV was serologically related, but not identical, to several insect nodaviruses. The single capsid protein of MwV was 40,000 MW, the same as black beetle virus (BBV), but virus particles had a different electrophoretic mobility from BBV. The bipartite RNA genome, like other nodaviruses, consisted of two species of MW 1.1 and 0.46 million. MwV particles sedimented at 142 S and had an estimated density in neutral CsCl of 1.366 g/ml compared with 1.352 g/ml for BBV. The serological and physico-chemical properties, compared with other nodaviruses, indicate that MwV is unique.
SUMMARYRecombinant and parental poliovirus particles were indistinguishable by ratezonal and isopycnic sedimentation, and by u.v. inactivation. Sensitive selective procedures, applied to ts + recombinants to detect genetic segregation of one parent, failed to reveal any. Poliovirus genetic recombinant particles thus appear to be conventional virus particles; their significance for recombination mechanisms is discussed. Sensitivity to the growth inhibitor 2-(3-chloro-p-tolyl)-5-ethyl-l,3,4-oxadiazole is shown to depend on a product of the structural protein gene.
This paper presents evidence thatThe sequences indicate that the pre-protein is cleaved at two positions to produce the 56 and 6 kDa capsid proteins as well as a predicted third protein that was not detected in the mature virion. Phylogenetic analysis of the capsid proteins indicated that TaV is more closely related to NβV than to the Nudaurelia ω-like viruses. The eight β-sheets that make up a jelly roll structure in the TaV capsid protein were identified by computer analysis.
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