Identification and characterization of a conserved baculoviral structural protein ODVP-6E/ODV-E56 from Choristoneura fumiferana granulovirus

Polydnavirus hidden face: the genes producing virus particles of parasitic wasps

Very few obligatory relationships involve viruses to the remarkable exception of polydnaviruses (PDVs) associated with tens of thousands species of parasitic wasps that develop within the body of lepidopteran larvae. PDV particles, injected along with parasite eggs into the host body, act by manipulating host immune defences, development and physiology, thereby enabling wasp larvae to survive in a potentially harmful environment. Particle production does not occur in infected tissues of parasitized caterpillars, but is restricted to specialized cells of the wasp ovaries. Moreover, the genome enclosed in the particles encodes almost no viral structural protein, but mostly factors used to manipulate the physiology of the parasitized host. We recently unravelled the viral nature of PDVs associated with braconid wasps by characterizing a large set of nudivirus genes residing permanently in the wasp chromosome(s). Many of these genes encode structural components of the bracovirus particles and their expression pattern correlates with particle production. They constitute a viral machinery comprising a large number of core genes shared by nudiviruses and baculoviruses. Thus bracoviruses do not appear to be nudiviruses remnants, but instead complex nudiviral devices carrying DNA for the delivery of virulence genes into lepidopteran hosts. This highlights the fact that viruses should no longer be exclusively considered obligatory parasites, and that in certain cases they are obligatory symbionts.

Location and phylogenetic analysis of the region immediately upstream of the granulin gene of the Clostera anachoreta granulovirus

The region immediately upstream of the granulin gene from Clostera anachoreta granulovirus (ClanGV) was identified from hybridization experiments and sequenced. The sequence of 5122nt EcoRI restriction fragment was presented and compared with the equivalent area in other GVs. Database searches showed that this region contained three open reading frames (ORFs) similar to the baculovirus genes (egt, fgf and me53, respectively) and four ORFs unique to ClanGV genome. Phylogenetic trees of the baculovirus genes egt and me53 were constructed. These analyses indicated that ClanGV genes may be more closely related to CfGV, CpGV, ClGV, PoGV and AoGV than to PxGV and XcGV.

Identification, transcriptional and phylogenetic analysis of the DNA polymerase gene of Pieris rapae granulovirus

The DNA polymerase gene (dnapol) of the Pieris rapae granulovirus (PiraGV) was completely sequenced and located between 73.1 and 76 m.u. on the PiraGV genome. Its open reading frame (ORF) has 3135 nucleotides (35% G-C content) encoding 1045 amino acids with a predicted molecular mass of 122.16 kDa. Homology analysis indicated that PiraGV dnapol had 28-66% amino acid identity to that of other known baculoviruses. Comparative sequence analyses demonstrated that the PiraGV dnapol gene contains conserved 3'-5' exonuclease motifs and DNA binding functional domains of the DNA polymerase enzyme found in all known baculovirus dnapols. Northern blot results showed that in infected Pieris rapae larvae the PiraGV dnapol gene was transcribed as a predominant 3.7 kb mRNA. 5' and 3' RACE indicated that the PiraGV dnapol transcript was initiated from the thymine residue located at -378 nt upstream from the ATG start codon and terminated at the polyadenylation signal AATAAA. Phylogenetic analysis of dnapol sequences suggests that the PiraGV dnapol is more closely related to that of Cydia pomonella GV and Cryptophlebia leucotreta GV than to those of other baculoviruses.

Choristoneura fumiferana Granulovirus pk-1: a baculoviral protein kinase

Open reading frame (ORF) 3 on the Choristoneura fumiferana granulovirus (ChfuGV), located in the 11 kb fragment of the BamHI genomic bank encodes a predicted 32-kDa putative kinase protein. Bioinformatics analysis on the predicted amino acid sequence of ChfuGV PK-1 revealed the existence of 11 catalytic subdomains. Sequence analysis within the 5'-untranslated region (5'-UTR) of ChfuGV pk- 1 indicates the presence of both putative early and late promoter motifs, indicating that pk-1 may be expressed throughout the infection cycle. Promoter sequence analysis reveals that pk-1 is deprived of a TATA box and appears instead to be regulated by other cis-acting transcriptional regulatory elements. Temporal transcription analysis by RT-PCR confirms the appearance of transcripts detected from 2 h p.i. until 72 h p.i. Northern blot hybridization characterizes pk-1 transcription as a 1.2 kb transcript. Homology comparisons reveal that ChfuGV PK-1 protein is most closely related to Phthorimaea operculalla granulovirus (PoGV) with 80 % amino acid identity.

Transcription, Translation, and Immunolocalization of ODVP-6E/ODV-E56 and p74 Proteins: Two Highly Conserved ODV-associated Envelope Proteins of Choristoneura fumiferana Granulovirus

Choristoneura fumiferana granulovirus (ChfuGV) infection results two types of enveloped virions: Occlusion-derived virus (ODV) and budded virus (BV). Structural proteins ODVP-6E/ODV-E56 and p74 are two major conserved ODV-associated proteins that may be involved in the initiation of viral infection cycle in susceptible host insect larvae. This study presents the characterization of ChfuGV odvp-6e/odv-e56 and p74 transcription and translation as well as immunolocalization of these proteins in the occluded ChfuGV virion. Our results revealed that the transcription of odvp-6e/odv-e56 and p74 genes, both, start at 24 hours post infection (h p.i.). Using monospecific polyclonal antibodies made against ODVP-6E/ODV-E56 and p74 we demonstrated that these proteins are both expressed late in infection (24 h p.i.). Immunogold labeling using antisera against ODVP-6E/ODV-E56 and p74 proteins demonstrated that ODVP-6E/ODV-E56 and p74 proteins are both associated with the ODV envelop of ChfuGV.

Choristoneura fumiferana Granulovirus p74 protein, a highly conserved baculoviral envelope protein

A gene that encodes a homologue to baculoviral p74, an envelope-associated viral structural protein, has been identified and sequenced on the genome of Choristoneura fumiferana granulovirus (ChfuGV). A part of the ChfuGV p74 gene was located on an 8.9 kb BamHI subgenomic fragment using different sets of degenerated primers. These were designed using the results of the protein sequencing of a major 74 kDa structural protein that is associated with the occlusion-derived virus (ODV). The gene has a 1992 nucleotide (nt) open-reading frame (ORF) that encodes a protein with 663 amino acids with a predicted molecular mass of 74,812 Da. Comparative studies revealed the presence of two major conserved regions in the ChfuGV p74 protein. This study also shows that all of the p74 proteins contain two putative transmembrane domains at their C-terminal segments. At the nucleotide sequence level, two late promoter motifs (TAAG and GTAAG) were located upstream of the first ATG of the p74 gene. The gene contained a canonical poly(A) signal, AATAAA, at its 3 non-translated region. A phylogenetic tree for baculoviral p74 was constructed using a maximum parsimony analysis. The phylogenetic estimation demonstrated that ChfuGV p74 is related the closest to those of Cydia pomonella granulovirus (CpGV) and Phthorimaea operculella granulovirus (PhopGV).