Sequence analysis of the genome of the Neodiprion sertifer nucleopolyhedrovirus

Proteins associated with Culex nigripalpus nucleopolyhedrovirus occluded virions

Occlusion-derived virions (ODVs) of the nucleopolyhedrovirus of Culex nigripalpus (CuniNPV) were purified by Ludox density gradient ultracentrifugation, and the proteins were separated by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Proteins were identified by using Edman sequencing, matrix-assisted laser desorption ionization-time of flight mass spectrometry, nanoelectrospray quadrupole time-of-flight mass spectrometry, or a combination of these methods. Half of the 44 polypeptide sequences identified in this analysis were unique open reading frames (ORFs) encoded by the CuniNPV genome and did not show similarity to any other sequences present in protein databases. Of the 22 polypeptides that showed similarities to other baculovirus-encoded proteins, only 17 sequences have previously been identified as structural proteins. The newly identified CuniNPV structural proteins cun058, cun059, cun087, cun106, and cun109 are homologues of Autographa californica nucleopolyhedrovirus (AcMNPV) ORFs 68, 62, 98, 81, and 2, respectively. The products of four genes, namely, lef-1 (cun045), alkaline exonuclease (cun054), helicase (cun089), and DNA polymerase (cun091), were not detected in the CuniNPV ODV preparations. These four genes are conserved among all annotated baculovirus genomes, and their homologues have been detected in the ODV of AcMNPV.

The baculoviruses occlusion-derived virus: virion structure and function

Baculoviruses play an important ecological role regulating the size of insect populations. For many years, baculoviruses have been applied as targeted biocontrol agents against forestry and agriculture pests. Baculovirus insecticides are effective against insect pests such as velvetbean caterpillar (Anticarsia gemmatalis ), cotton bollworm (Helicoverpa zea ), and gypsy moth (Lymantria dispar ). Baculoviruses are transmitted to insects by the oral route mediated by the occlusion-derived virus (ODV). The ODV is also specialized to exploit the insect midgut that is one of the most extreme biological environments where the viruses are subject to caustic pH and digestive proteases. The molecular biology of the ODV reveals new frontiers in protein chemistry. Finally, ODVs establishes infection in insect gut tissues that are virtually nonsupportive to virus replication and which are continuously sloughed away. ODVs carry with them a battery of proteins that enable them to rapidly exploit and harness these unstable cells for virus replication.

Mosquito pathogenic viruses--the last 20 years

There are several types of viral pathogens that cause disease in mosquitoes with most belonging to 4 major groups. The most common viruses of mosquitoes are the baculoviruses (NPVs) (Baculoviridae: Nucleopolyhedrovirus) and cytoplasmic polyhedrosis viruses (CPVs) (Reoviridae: Cypovirus). The other major types of viruses in mosquitoes are represented by the densoviruses (DNVs) (Parvoviridae: Brevidensovirus) and the iridoviruses (MIVs) (Iridoviridae: Chloriridovirus). Baculoviruses, densoviruses and iridoviruses are DNA viruses while cypoviruses are the main RNA viruses in mosquitoes. This chapter presents an overview of the recent advancements in the study of mosquito pathogenic viruses and discusses how this new understanding of virus-mosquito interactions can be used to develop novel research and control strategies.

Genome of the most widely used viral biopesticide: Anticarsia gemmatalis multiple nucleopolyhedrovirus

The genome of Anticarsia gemmatalis multiple nucleopolyhedrovirus isolate 2D (AgMNPV-2D), which is the most extensively used virus pesticide in the world, was completely sequenced and shown to have 132 239 bp (G+C content 44.5 mol%) and to be capable of encoding 152 non-overlapping open reading frames (ORFs). Three ORFs were unique to AgMNPV-2D, one of which (ag31) had similarity to eukaryotic poly(ADP-ribose) polymerases. The lack of chiA and v-cath may explain some of the success and growth of the AgMNPV biological control programme, as it may explain the high recovery of polyhedra sequestered inside dead larvae in the field, which are collected and used for further application as biological pesticides in soybean fields. The genome organization was similar to that of the Choristoneura fumiferana defective MNPV (CfDefNPV). Most of the variation between the two genomes took place near highly repetitive regions, which were also closely associated with bro-coding regions. The separation of the NPVs into groups I and II was supported by: (i) a phenogram of the complete genomes of 28 baculovirus and Heliothis zea virus 1, (ii) the most parsimonious reconstruction of gene content along the phenograms and (iii) comparisons of genomic features. Moreover, these data also reinforced the notion that group I of the NPVs can be split further into the AgMNPV lineage (AgMNPV, CfDefNPV, Epiphyas postvittana NPV, Orgyia pseudotsugata MNPV and C. fumiferana MNPV), sharing eight defining genes, and the Autographa californica MNPV (AcMNPV) lineage (AcMNPV, Rachiplusia ou NPV and Bombyx mori NPV), sharing nine defining genes.

Genome sequence and organization of a nucleopolyhedrovirus that infects the tea looper caterpillar, Ectropis obliqua

The complete nucleotide sequence of Ectropis obliqua nucleopolyhedrovirus (EcobNPV), which infects the tea looper caterpillar, was determined and analyzed. The double stranded circular genome is composed of 131,204 bp and is 37.6% G+C rich. The analysis predicted 126 putative, minimally overlapping open reading frames (ORFs) with 150 or more nucleotides that together compose 89.8% of the genome. The remaining 10.2% constitute non-coding and three homologous regions. Comparison with previously sequenced baculoviruses indicated that three ORFs were unique to EcobNPV, while the remaining 123 ORFs shared identity with other baculovirus genes. In addition to two bro homologues, three other repeat ORFs, including dbp, p26, and odv-e66, were identified. Phylogenetic analysis indicated that each member of the paired ORFs was acquired independently. Gene parity plot analysis and percent identity of gene homologues suggested that EcobNPV is a Group II NPV, although its genomic organization was highly distinct.

Characterization of Antheraea pernyi nucleopolyhedrovirus p11 gene, a homologue of Autographa californica nucleopolyhedrovirus orf108

Antheraea pernyi nucleopolyhedrovirus (ApNPV) p11 gene is 309 bp long, potentially encoding 102 amino acids with a predicted molecular weight of 11.2 kDa. ApNPV p11 gene was cloned into the prokaryotic expression vector pQE-30 and P11 was expressed in E. coli M15. Polyclonal antiserum was made against 6xHis tagged P11 protein expressed in E. coli M15. P11 gene transcription was detected as early as 36 h post-infection (p.i.) in tussah pupa and remain at high level up to 96 h p.i. Structural localization revealed that P11 protein was present in polyhedral inclusion bodies (PIB) dilute alkaline saline (DAS) pellet (P) fractions and occlusion-derived virus (ODV), but not in PIB DAS supernatant (S) fractions and budded virus (BV). These results indicated that P11 was associated with ApNPV structure.

Autographa californica multiple nucleopolyhedrovirus nucleocapsid assembly is interrupted upon deletion of the 38K gene

38K (ac98) of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is a highly conserved baculovirus gene whose function is unknown. To determine the role of 38K in the baculovirus life cycle, a 38K knockout bacmid containing the AcMNPV genome was generated through homologous recombination in Escherichia coli. Furthermore, a 38K repair bacmid was constructed by transposing the 38K open reading frame with its native promoter region into the polyhedrin locus of the 38K knockout bacmid. After transfection of these viruses into Spodoptera frugiperda cells, the 38K knockout bacmid led to a defect in production of infectious budded virus, while the 38K repair bacmid rescued this defect, allowing budded-virus titers to reach wild-type levels. Slot blot analysis indicated that 38K deletion did not affect the levels of viral DNA replication. Subsequent immunoelectron-microscopic analysis revealed that masses of electron-lucent tubular structures containing the capsid protein VP39 were present in cells transfected with 38K knockout bacmids, suggesting that nucleocapsid assembly was interrupted. In contrast, the production of normal nucleocapsids was restored when the 38K knockout bacmid was rescued with a copy of 38K. Recombinant virus that expresses 38K fused to green fluorescent protein as a visual marker was constructed to monitor protein transport and localization within the nucleus during infection. Fluorescence was first detected along the cytoplasmic periphery of the nucleus and subsequently localized to the center of the nucleus. These results demonstrate that 38K plays a role in nucleocapsid assembly and is essential for viral replication in the AcMNPV life cycle.

Prospects for the mosquito baculovirus CuniNPV as a tool for mosquito control

CuniNPV is a pathogen of Culex mosquitoes, vectors of West Nile virus and other forms of encephalitis. Successful development of CuniNPV requires an efficient production system and formulated product that incorporates magnesium, an essential component for transmission. It may be possible to develop mosquito baculoviruses as a new type of biopesticide by microencapsulating the virus and magnesium into formulations that would be effective regardless of the water quality. In addition, this new insight on transmission may facilitate the discovery and development of additional baculoviruses for the control of other important mosquito vectors. Biological mining of the CuniNPV genome and investigations to understand virus-mosquito interactions at the molecular level offer exciting possibilities for the development of novel mosquito control strategies and tools. Understanding the molecular mechanisms of infection will provide the opportunity to devise new control strategies, for example, compromising the defensive systems of the mosquito (proteases for the peritrophic matrix) or exploiting receptors used by the virus to specifically deliver toxins to mosquito larvae via the midgut. As additional baculovirus genomes become available, comparative genomics could lead to a more informed understanding of how the virus exploits its host as well as the factors responsible for the genus-specific host range of most known mosquito baculoviruses.

Sequence analysis and organization of the Neodiprion abietis nucleopolyhedrovirus genome

Of 30 baculovirus genomes that have been sequenced to date, the only nonlepidopteran baculoviruses include the dipteran Culex nigripalpus nucleopolyhedrovirus and two hymenopteran nucleopolyhedroviruses that infect the sawflies Neodiprion lecontei (NeleNPV) and Neodiprion sertifer (NeseNPV). This study provides a complete sequence and genome analysis of the nucleopolyhedrovirus that infects the balsam fir sawfly Neodiprion abietis (Hymenoptera, Symphyta, Diprionidae). The N. abietis nucleopolyhedrovirus (NeabNPV) is 84,264 bp in size, with a G+C content of 33.5%, and contains 93 predicted open reading frames (ORFs). Eleven predicted ORFs are unique to this baculovirus, 10 ORFs have a putative sequence homologue in the NeleNPV genome but not the NeseNPV genome, and 1 ORF (neab53) has a putative sequence homologue in the NeseNPV genome but not the NeleNPV genome. Specific repeat sequences are coincident with major genome rearrangements that distinguish NeabNPV and NeleNPV. Genes associated with these repeat regions encode a common amino acid motif, suggesting that they are a family of repeated contiguous gene clusters. Lepidopteran baculoviruses, similarly, have a family of repeated genes called the bro gene family. However, there is no significant sequence similarity between the NeabNPV and bro genes. Homologues of early-expressed genes such as ie-1 and lef-3 were absent in NeabNPV, as they are in the previously sequenced hymenopteran baculoviruses. Analyses of ORF upstream sequences identified potential temporally distinct genes on the basis of putative promoter elements.

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.

Sequence analysis of the Choristoneura occidentalis granulovirus genome

The genome of the Choristoneura occidentalis granulovirus (ChocGV) isolated from the western spruce budworm, Choristoneura occidentalis, was sequenced completely. It was 104,710 bp long, with a 67.3% A+T content and contained 116 potential open reading frames (ORFs) covering 88.4% of the genome. Of these, 29 ORFs were conserved in all fully sequenced baculovirus genomes, 30 were GV-specific, 53 were present in some nucleopolyhedroviruses (NPVs) and/or GVs, three were common to ChocGV and Choristoneura fumiferana GV (ChfuGV) and one was so far unique. To date, ChocGV is the only GV identified that contains a homologue of the apoptosis inhibitor protein P35/P49, present in some group I NPVs. It is also the first GV without a Xestia c-nigrum GV ORF 26 homologue. Five homologous regions (hrs)/repeat regions, lacking typical NPV hr palindromes were identified. ChocGV hrs were similar to each other but not to other GV hrs. A 1.8 kb repeat region with a high A+T content (81%) and multiple repeats of 21-210 bp was found between choc36 and 37. This area resembled the non-homologous region origin of DNA replication (non-hr ori) identified in Cryptophlebia leucotreta GV (CrleGV) and Cydia pomonella GV (CpGV). Based on the mean amino acid identities of homologous proteins, ChocGV was closest to fully sequenced genomes CpGV (52.3%) and CrleGV (52.1%). The closest amino acid identity was to individual ORFs from the partially sequenced ChfuGV genome (97.2% in 38 ORFs). Phylogenetic analysis placed ChocGV in a clade with CrleGV and CpGV.

In vivo and in vitro analyses of a Bombyx mori nucleopolyhedrovirus mutant lacking functional vfgf

All lepidopteran baculovirus genomes sequenced to date encode a viral fibroblast growth factor homolog (vfgf), suggesting that vfgf may play an important role in the infection cycle of lepidopteran baculoviruses. Here, we describe the characterization of a Bombyx mori nucleopolyhedrovirus (BmNPV) mutant lacking functional vfgf. We constructed a vfgf deletion mutant (BmFGFD) and characterized it in BmN cells and B. mori larvae. We observed that budded virus (BV) production was reduced in BmFGFD-infected BmN cells and B. mori larvae. The larval bioassays also revealed that deletion of vfgf did not reduce the infectivity; however, the mutant virus did take 20 h longer to kill B. mori larvae than wild-type BmNPV, when tested either by BV injection or by polyhedrin-inclusion body ingestion. These results suggest that BmNPV vfgf is involved in efficient virus production in BmN cells and B. mori larvae.

Function of Spodoptera exigua nucleopolyhedrovirus late gene expression factors in the insect cell line SF-21

We used a well established transient expression assay to test the ability of the baculovirus Spodoptera exigua M nucleopolyhedrovirus (SeMNPV) homologs of Autographa californica MNPV (AcMNPV) late expression factors (lefs) to activate a late promoter-reporter gene cassette in SF-21 cells. This insect-derived cell line is fully permissive for AcMNPV infection but not for SeMNPV. In the assay, 19 AcMNPV lefs stimulate optimal levels of late gene promoter activity. SeMNPV lef-5 successfully replaced the corresponding AcMNPV gene in the context of the remaining set of AcMNPV lefs, whereas SeMNPV dnapol and 39k exhibited partial activity. When all the SeMNPV lefs were assayed together or in the presence of four lefs encoded only in AcMNPV, it resulted in background levels of late promoter-driven reporter gene activity. However, SeMNPV genomic DNA and the four AcMNPV-specific lefs stimulated low levels of reporter gene activity. Moreover, SeMNPV IE-1, but not AcMNPV IE-1, further stimulated late gene expression in the presence of SeMNPV DNA. AcMNPV IE-1 was able to mediate early gene expression cis-linked to homologous regions (hrs) derived from AcMNPV and SeMNPV. In contrast, SeMNPV IE-1 was more specific for SeMNPV-derived hr elements.

Characterization of Spodoptera exigua multicapsid nucleopolyhedrovirus ORF100 and ORF101, two homologues of E. coli ChaB

ChaB, a putative regulator of ChaA in Escherichia coli (E. coli), and its homologues constitute a multigene family known to occur among bacteria, archaeabacteria and baculoviruses. The baculovirus Spodoptera exigua multicapsid nucleopolyhedrovirus contains two homologues of E. coli ChaB, open reading frames (ORFs) 100 (Se100) and 101 (Se101). RT-PCR and 5' RACE analyses indicated that transcription of both SeMNPV chaB genes occurs by 24 h postinfection and is initiated at a late consensus ATAAG motif. Immunoblot analysis showed that Se100 and Se101 were, respectively, expressed as 11 and 28kDa proteins in infected cells, and they were distributed in both cytoplasm and nucleus. Further analysis revealed that Se100 and Se101 are associated with nuclear structure and only present in the nucleocapsid of occlusion-derived virus. Additionally, column chromatography analysis showed that both proteins could weakly interact with nucleic acids. It was proposed that SeMNPV ChaB might function as DNA binding proteins.

On the classification and nomenclature of baculoviruses: A proposal for revision

Recent evidence from genome sequence analyses demands a substantial revision of the taxonomy and classification of the family Baculoviridae. Comparisons of 29 baculovirus genomes indicated that baculovirus phylogeny followed the classification of the hosts more closely than morphological traits that have previously been used for classification of this virus family. On this basis, dipteran- and hymenopteran-specific nucleopolyhedroviruses (NPV) should be separated from lepidopteran-specific NPVs and accommodated into different genera. We propose a new classification and nomenclature for the genera within the baculovirus family. According to this proposal the updated classification should include four genera: Alphabaculovirus (lepidopteran-specific NPV), Betabaculovirus (lepidopteran-specific Granuloviruses), Gammabaculovirus (hymenopteran-specific NPV) and Deltabaculovirus (dipteran-specific NPV).

Conserved molecular systems of the Baculoviridae

Although the Baculoviridae are a large and diverse family of viruses, they are united by a number of shared features that form the basis for their unique life cycle. These include the mechanism of cell entry, genome replication and processing, and late and very late gene transcription. In this review, the molecular systems that are conserved within the Baculoviridae and that are responsible these processes are described.

Characterization of two homologues of ChaB in Spodoptera litura multicapsid nucleopolyhedrovirus

ChaB, a putative regulator of ChaA in Escherichia coli (E. coli), and its homologues constitute a multigene family known to occur among bacteria, archaeabacteria and baculoviruses. Distinguished from E. coli ChaB, baculoviruses ChaB proteins lack a charged loop that can bind to Ca2+ and Mg2+. The baculovirus Spodoptera litura multicapsid nucleopolyhedrovirus (SpltMNPV) contains two homologues of ChaB, open reading frames (ORFs) 52 (Sl52) and 53 (Sl53). Reverse transcription-PCR and 5' Race analyses indicated that transcription of both SpltMNPV chaB genes occurs by 12 h postinfection and is initiated at a late consensus (A/T)TAAG motif. Immunoblot analysis showed that Sl52 was expressed as a doublet of 23 and 26 kDa in infected S. litura cells, while Sl53 was expressed as a 16 kDa protein. Biochemical fractionation analysis indicated that the 23 kDa form of Sl52 was distributed in both cytoplasm and nucleus of infected cells, whereas the 26 kDa form of Sl52 and Sl53 proteins were only present in nucleus. Further analysis revealed that these proteins are associated with the nucleocapsid of occlusion-derived virus. Using a histone extraction protocol, the Sl53 and 26 kDa form of Sl52 proteins were both detected in the histone H1 fraction. Additionally, column chromatography analysis showed that the Sl52 and Sl53 proteins could interact with nucleic acids. It was proposed that SpltMNPV ChaB might function as DNA binding proteins.

Analysis of a baculovirus lacking a functional viral fibroblast growth factor homolog

Baculoviruses encode fibroblast growth factor (vfgf) homologs whose function during virus infection is unknown. We constructed a recombinant bacmid of Autographa californica M nucleopolyhedrovirus (AcMNPV) lacking a functional vfgf and characterized it in two insect cell lines. The kinetics of budded virus production were similar in the parental and vfgf-deficient viruses in both cell lines at both high and low multiplicities of infection. In addition, no obvious differences were observed between the mutant and parental viruses in protein or DNA synthesis. Finally, coinfection of vfgf-containing and -deficient viruses and passage for several generations did not reveal a consistent growth advantage for either virus.

Identification and characterization of odv-e25 of Spodoptera litura multicapsid nucleopolyhedrovirus

Spodoptera litura multicapsid nucleopolyhedrovirus (SpltMNPV) odv-e25 is 684 bp long, potentially encoding 227 amino acids with a predicted molecular weight of 24.9 kDa. Homology analysis indicated that SpltMNPV ODV-E25 has 35-65% amino acid identity with that of other known baculoviruses. RT-PCR results revealed that the odv-e25 is transcribed actively at the late stage of infection and the mRNA start site was mapped within a consensus baculovirus late promoter sequence (TTAAG). Western blot analysis of odv-e25 expression with an antiserum made against 6 x His tagged ODV-E25 expressed in Escherichia coli indicated that it was present as a doublet of approximately 27 kDa from 24 h through 96 h in SpltMNPV-infected Spli-221 cells. Similar results were seen on Western blots of Spodoptera exigua (Se)MNPV-infected Se301 cells. Immunofluorescence analysis showed that ODV-E25 was predominantly present in the cytoplasm of SpltMNPV-infected cells and localized to the envelopes of occlusion-derived virus.

Identification of Spodoptera Litura Multicapsid Nucleopolyhedrovirus ORF97, A Novel Protein Associated with Envelope of Occlusion-derived Virus

Open reading frame (ORF) 97 of Spodoptera litura multicapsid nucleopolyhedrovirus (Splt97) is a member of 11k gene family (InterPro database accession number: IPR009313) in insect viruses, potentially encoding 112 amino acids with a predicted molecular weight of 13.2 kDa. Sequence analysis indicated that Splt97 has 8-50% amino acid identity with the homologues of other known baculoviruses including Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) ORF108. Splt97 transcription in SpltMNPV-infected Spli-221 cells was detected from 6 to 96 h postinfection (p.i.) and the mRNA start site was mapped within a consensus baculovirus early promoter motif (ACATT). Time course of Splt97 expression in SpltMNPV-infected cells showed that Splt97 was expressed from 48 through 96 h p.i. as a 13 kDa protein. Western blot analysis revealed that Splt97 was present in occlusion-derived virus (ODV). Furthermore, when ODV was fractionated into nucleocapsid and envelope components, Splt97 was shown to be present only in the envelope. These results suggested that Splt97 was a baculovirus ODV-associated protein.

Molecular identification and phylogenetic analysis of baculoviruses from Lepidoptera

PCR amplification of the highly conserved baculovirus genes late expression factor 8 (lef-8), late expression factor 9 (lef-9) and polyhedrin/granulin (polh/gran) combined with molecular phylogenetic analyses provide a powerful tool to identify lepidopteran-specific baculoviruses and to study their diversity. In the present investigation, we have improved the degenerate oligonucleotides and corroborated the approach that was recently described by Lange et al. (Lange, M., Wang, H., Zhihong, H., Jehle, J.A., 2004. Towards a molecular identification and classification system of lepidopteran-specific baculoviruses. Virology 325, 36-47.). Baculovirus DNA was isolated from 71 uncharacterized historic baculovirus samples, and partial gene sequences were amplified by using gene-specific degenerate PCR primers. The obtained PCR products were directly sequenced, and the deduced amino acid sequences were compiled and aligned with published sequences of these target genes. A phylogenetic tree of 117 baculoviruses was inferred using maximum parsimony and distance methods. Based on the comprehensive phylogenetic analysis of the partial lef-8, lef-9 and polh/gran genes, we propose a phylogenetic species criterion for lepidopteran-specific baculoviruses that uses the genetic distances of these genes for species demarcation.

Baculoviruses-- re-emerging biopesticides

Biological control of agricultural pests has gained importance in recent years due to increased pressure to reduce the use of agrochemicals and their residues in the environment and food. Viruses of a few families are known to infect insects but only those belonging to the highly specialized family Baculoviridae have been used as biopesticides. They are safe to people and wildlife, their specificity is very narrow. Their application as bioinsecticides was limited until recently because of their slow killing action and technical difficulties for in vitro commercial production. Two approaches for the wider application of baculoviruses as biopesticides will be implemented in future. In countries where use of genetically modified organisms is restricted, the improvements will be mainly at the level of diagnostics, in vitro production and changes in biopesticide formulations. In the second approach, the killing activity of baculoviruses may be augmented by genetic modifications of the baculovirus genome with genes of another natural pathogen. It is expected that the baculoviruses improved by genetic modifications will be gradually introduced in countries which have fewer concerns towards genetically modified organisms.

Functional analysis of evolutionary conserved clustering of bZIP binding sites in the baculovirus homologous regions (hrs) suggests a cooperativity between host and viral transcription factors

The genome of the Autographa californica Multinucleocapsid Polyhedrosis Virus (AcMNPV) contains nine interspersed homologous regions (hrs) that function as potent enhancer sequences when linked in cis to either viral or heterologous RNA polymerase II-dependent promoters. Their activity is strongly increased by the binding of the major immediate early viral transregulator IE1 on 28-mer palindromic sites present in hrs. We show that hrs of AcMNPV additionally carry, in the interpalindromic sequences, a large number of cAMP response elements (CRE) and TPA response elements (TRE), known to bind ubiquitous cellular transcription factors of the bZIP family. Moreover, these clusters of CRE and TRE motifs are concentrated in hrs. Analysis of the 25 baculovirus genomes sequenced so far reveals that these motifs are evolutionary conserved in Lepidoptera NPVs, suggesting a functional role in the hr enhancer function. Consistently, EMSA experiments indicate that CRE and on a lesser extent TRE sites specifically bind insect host factors. Moreover, reporter assays reveal that these CRE sites have an additive stimulatory effect on RNAPol II-dependent transcription in Sf9 cells and are potentially able to synergize with the IE1-binding palindrome.

A cellular Drosophila melanogaster protein with similarity to baculovirus F envelope fusion proteins

Baculovirus F (fusion) proteins are found in the envelopes of budded virions. Recently a Drosophila melanogaster gene (CG4715) that encodes a protein with sequence similarity to baculovirus F proteins was discovered. To examine similarities and differences with baculovirus F proteins, we cloned the D. melanogaster cellular F (Dm-cF) protein gene and analyzed Dm-cF expression and localization. The predicted Dm-cF protein sequence lacks a furin cleavage site, and transiently expressed Dm-cF showed no protein cleavage and no detectable membrane fusion activity. In cell localization studies, transiently expressed Dm-cF was localized to intracellular organelles in D. melanogaster S2 cells, unlike baculovirus F proteins, which localize to cellular plasma membranes. Using reverse transcriptase PCR and Western blot analysis to examine Dm-cF expression in animals, we detected Dm-cF expression in both larval and adult D. melanogaster cells. However, Dm-cF expression was detected only in third instar larvae and adults, suggesting that Dm-cF expression may be developmentally regulated. We also identified genes related to Dm-cF in the genomes of two other Drosophila species, Drosophila yakuba and Drosophila pseudoobscura, and the mosquito Anopheles gambiae. These observations suggest that f genes may be present in the genomes of many insects. Conservation within and between 22 baculovirus and 4 insect F proteins was examined in detail. These studies demonstrate that Dm-cF is expressed in D. melanogaster and suggest that if baculovirus f genes are derived from a host cellular f gene, the function appears to have changed substantially upon adaptation to the baculovirus infection cycle.

Genome sequence of Chrysodeixis chalcites nucleopolyhedrovirus, a baculovirus with two DNA photolyase genes

The complete genome sequence of a single nucleocapsid nucleopolyhedrovirus recently isolated from Chrysodeixis chalcites (ChchNPV) was determined. The viral genome has a size of 149 622 bp and an overall G+C content of 39.1 mol%. The sequence contains 151 predicted open reading frames (ORFs) with a minimal size of 50 codons. The similarity of these ORFs with those of other completely sequenced baculoviruses was calculated using a newly developed database, named GECCO. Phylogenetic analysis of the whole genome confirmed the evolutionary relationship of ChchNPV with group II NPVs, as did the absence of the NPV group I-specific gp64 gene. It is the first group II NPV to encode proliferating cell nuclear antigen. Most noteworthy is the presence of two ORFs encoding a class II cyclobutane pyrimidine dimer DNA photolyase. These two ORFs share only 45 % amino acid identity and have different promoter motifs. Twenty-two additional unique baculovirus genes were identified, including a gene encoding a novel putative RING finger protein with a possible homologue in poxviruses.

Stimulation of cell motility by a viral fibroblast growth factor homolog: proposal for a role in viral pathogenesis

The Autographa californica M nucleopolyhedrovirus (AcMNPV) encodes a gene (open reading frame 32) with homology to vertebrate and invertebrate fibroblast growth factors (fgfs), key regulators of developmental processes affecting the growth, differentiation, and migration of many cell types. We studied the temporal regulation of the AcMNPV fgf, vfgf, by Northern (RNA) blot hybridization; vfgf was transcribed as a 0.6-kb mRNA at early times but as part of a 1.4-kb bicistronic mRNA at late times. The product of vfgf, vFGF, exhibited a number of characteristics that have also been demonstrated for other FGF homologs. vFGF had strong affinity to heparin, a property important for FGF signaling via an FGF receptor. vFGF was secreted into the extracellular fluid when expressed in insect cells, suggesting that it acts as an extracellular ligand. Finally, vFGF was able to stimulate migration of several different types of insect cells. We discuss how this activity may be important for its function during virus infection.

Identification of functional domains required for HearNPV P10 filament formation

Baculovirus encoded P10 form fibrillar structures in infected cells. We have tried to identify the functional domains for the P10 filament formation by green fluorescence protein (GFP) tag. The p10 gene of Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HearNPV) was the subject of these studies. Different lengths of HearNPV p10 gene were constructed with GFP fused in frame to the C-terminus. The constructs were transfected into insect and mammalian cells and observed by confocal microscopy. The results indicated that the first N-terminal 66 amino acids, which form the complete coiled-coil domain, were necessary for the aggregation and formation of filament structures of HearNPV P10. The proline-rich region and the C-terminal positively charged amino acids were not necessary for the formation of fibrillar structure but had some impact on the shape of the fibrillar structures. No other baculoviral proteins were needed for the formation of P10 filament structures in transfected cells.

Characterization of p24 Gene of Spodoptera litura Multicapsid Nucleopolyhedrovirus

Spodoptera litura multicapsid nucleopolyhedrovirus (SpltMNPV) p24 gene is 753 bp long, potentially encoding 244 amino acids with a predicted molecular weight of 27.3 kDa. Homology analysis indicated that SpltMNPV P24 has 20-36% amino acid identity with that of other known baculoviruses. RT-PCR results showed that the p24 gene is transcribed actively at the late stage of infection and the mRNA start site was mapped within a consensus baculovirus late promoter sequence (ATAAG). Western blot analysis of extracts from SpltMNPV-infected S. litura cells detected a specific 28 kDa protein, and this protein was not N-glycosylated. Structural localization revealed that SpltMNPV P24 was associated with the nucleocapsid of occlusion-derived virus (ODV) as a complex form of 83 kDa.

Comparison of the complete genome sequence between C1 and G4 isolates of the Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus

The complete nucleotide sequence of Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus isolate C1 (HearSNPV-C1) was determined and analyzed by comparing with the genome of HearSNPV-G4 isolate. C1 and G4 isolates occurred in the same host species and geographic location but showed different virulence. The HearSNPV-C1 genome consisted of 130,759 bp and 137 putative open reading frames larger than 150 nucleotides were identified. The two genomes shared 98.1% nucleotide sequence identity, with a total number of 555 bp substitutions, 1354 bp deletions, and 710 bp insertions in HearSNPV-C1. Comparison of ORFs and homologous repeat (hr) regions of the two genomes showed that there were four highly variable regions hr1, hr4, hr5, and bro-b, all in repeat regions. These results suggest that baculovirus strain heterogeneity may be often caused by SNPs and changes in the hrs and bro genes.

Gene organization and sequencing of the Choristoneura fumiferana defective nucleopolyhedrovirus genome

Two distinct nucleopolyhedrovirus species of the eastern spruce budworm, Choristoneura fumiferana, exist in a symbiont-like relationship. C. fumiferana defective nucleopolyhedrovirus (CfDEFNPV) only infects C. fumiferana larvae per os in the presence of C. fumiferana nucleopolyhedrovirus Ireland strain (CfMNPV), but is infective when injected into the haemolymph. CfDEFNPV synergizes CfMNPV in per os infections and CfMNPV is always the predominant progeny. This study was undertaken to report the genomic makeup and organization of CfDEFNPV in an attempt to identify its defect and understand its synergistic role. The genome was mapped, sequenced, characterized and compared to other baculoviruses. The CfDEFNPV genome was 131 160 nt long with 149 putative open reading frames (ORFs) and a G+C content of 45·8 mol%. Homologues of all 62 conserved lepidopteran baculovirus genes were found including those implicated in per os infectivity, p74, per os infectivity factor (pif) and pif-2. Although no obvious deletions were observed to explain the defect, two ORFs, Cfdef79 and Cfdef99 (inhibitor of apoptosis-4), contained potential deletions. Cfdef50 (late expression factor-10)/Cfdef51 (vp1054) and Cfdef76/Cfdef77 (telokin-like protein) had large overlaps and a potential homologue to ac105/he65 was split. Four baculovirus repeat ORFs were present, as were two unique genes, but no enhancins were identified. CfDEFNPV contained 13 homologous regions, each with one to five palindromes. Comparison with fully sequenced baculovirus genomes identified CfDEFNPV as a group I NPV with the closest average amino acid identity to Epiphyas postvittana NPV, followed by Orgyia pseudotsugata MNPV and CfMNPV, with its closest matches being to individual Anticarsia gemmatalis MNPV gene sequences.

Analysis of the Choristoneura fumiferana nucleopolyhedrovirus genome

The double-stranded DNA genome of Choristoneura fumiferana nucleopolyhedrovirus (CfMNPV) was sequenced and analysed in the context of other group I nucleopolyhedroviruses (NPVs). The genome consists of 129 593 bp with a G+C content of 50·1 mol%. A total of 146 open reading frames (ORFs) of greater than 150 bp, and with no or minimal overlap were identified. In addition, five homologous regions were identified containing 7–10 repeats of a 36 bp imperfect palindromic core. Comparison with other completely sequenced baculovirus genomes revealed that 139 of the CfMNPV ORFs have homologues in at least one other baculovirus and seven ORFs are unique to CfMNPV. Of the 117 CfMNPV ORFs common to all group I NPVs, 12 are exclusive to group I NPVs. Overall, CfMNPV is most similar to Orgyia pseudotsugata MNPV based on gene content, arrangement and overall amino acid identity. Unlike other group I baculoviruses, however, CfMNPV encodes a viral enhancing factor (vef) and has two copies of p26.

Functional analysis of the baculovirus host range gene, hrf-1

The hrf-1 gene from Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) prevents translation arrest and promotes Autographa californica multiple nucleopolyhedrovirus (AcMNPV) replication in IPLB-Ld652Y cells (Ld652Y), a non-permissive L. dispar cell line. There are no motifs in the predicted protein sequence to suggest how it might function and the only homolog identified is encoded by another baculovirus, Orgyia pseudotsugata multiple nucleopolyhedrovirus (OpMNPV). In this study, we report a functional analysis of the hrf-1 protein. AcMNPV bearing carboxy- or amino-terminally truncation hrf-1, and hrf-1 mutated by two-amino acid insertions did not replicate Ld652Y cells. Neither OpMNPV hrf-1 nor an OpMNPV/LdMNPV chimeric hrf-1 supported AcMNPV replication. Mutations in a highly acidic domain of hrf-1, in which aspartic acid residues were replaced with alanine, had varied effects on hrf-1 function. They had no effect, abolished hrf-1 function completely, or partially supported protein synthesis in infected Ld652Y cells. A slight increase in protein synthesis was achieved by increasing the expression of hrf-1 acidic domain mutant proteins. Together, these results indicate a critical role for hrf-1 structure and suggest a functional role for the acidic domain.

Sequence and organization of the Neodiprion lecontei nucleopolyhedrovirus genome

All fully sequenced baculovirus genomes, with the exception of the dipteran Culex nigripalpus nucleopolyhedrovirus (CuniNPV), have previously been from Lepidoptera. This study reports the sequencing and characterization of a hymenopteran baculovirus, Neodiprion lecontei nucleopolyhedrovirus (NeleNPV), from the redheaded pine sawfly. NeleNPV has the smallest genome so far published (81,755 bp) and has a GC content of only 33.3%. It contains 89 potential open reading frames, 43 with baculovirus homologues, 6 identified by conserved domains, and 1 with homology to a densovirus structural protein. Average amino acid identity of homologues ranged from 19.7% with CuniNPV to 24.9% with Spodoptera exigua nucleopolyhedrovirus. The conserved set of baculovirus genes has dropped to 29, since NeleNPV lacks an F protein homologue (ac23/ld130). NeleNPV contains 12 conserved lepidopteran baculovirus genes, including that for DNA binding protein, late expression factor 11 (lef-11), polyhedrin, occlusion derived virus envelope protein-18 (odv-e18), p40, and p45, but lacks 21 others, including lef-3, me53, immediate early gene-1, lef-6, pp31, odv-e66, few polyhedra 25k, odv-e25, protein kinase-1, fibroblast growth factor, and ubiquitin. The lack of identified baculovirus homologues may be due to difficulties in identification, differences in host-virus interactions, or other genes performing similar functions. Gene parity plots showed limited colinearity of NeleNPV with other baculoviruses, and phylogenetic analysis indicates that NeleNPV may have existed before the lepidopteran nucleopolyhedrovirus and granulovirus divergence. The creation of two new Baculoviridae genera to fit hymenopteran and dipteran baculoviruses may be necessary.