Virus in a parasitoid wasp: suppression of the cellular immune response in the parasitoid's host.

A virus that replicates in the ovary of a parasitoid wasp is injected into the parasitoid's host during oviposition. Successful development of th parasitoid egg within the host depends on the presence of th virus, which acts to suppress the host's immune response (encapsulation) toward the egg. This is an example of obligatory mutualism between a virus and a eukaryotic organism.

Trapping solid aerosols with optical tweezers: a comparison between gas and liquid phase optical traps.

We demonstrate a method for the optical trapping of solid aerosol particles. Suspension of silica particles in ethanol allows their delivery to the trapping volume using a commercial medical nebulizer. The ethanol quickly evaporates, leaving the solid particles trapped in air. We use the technique to make comparisons between aerosol and colloid tweezing through power spectra analysis of the particle's positions fluctuations for identical particles trapped in a water or air suspending medium.

Glycosylation and secretion of human tissue plasminogen activator in recombinant baculovirus-infected insect cells.

Cell lines established from the lepidopteran insect Spodoptera frugiperda (fall armyworm; Sf9) are used routinely as hosts for the expression of foreign proteins by recombinant baculovirus vectors. We have examined the pathway of protein glycosylation and secretion in these cells, using human tissue plasminogen activator (t-PA) as a model. t-PA expressed in Sf9 cells was both N glycosylated and secreted. At least a subset of the N-linked oligosaccharides in extracellular t-PA was resistant to endo-beta-N-acetyl-D-glucosaminidase H, which removes immature, high-mannose-type oligosaccharides. This refutes the general conclusion from previous studies that Sf9 cells cannot process immature N-linked oligosaccharides to an endo-beta-N-acetyl-D-glucosaminidase H-resistant form. A nonglycosylated t-PA precursor was not detected in Sf9 cells, even with very short pulse-labeling times. This suggests that the mammalian signal sequence of t-PA is efficiently recognized in Sf9 cells and that it can mediate rapid translocation across the membrane of the rough endoplasmic reticulum, where cotranslational N glycosylation takes place. However, t-PA was secreted rather slowly, with a half-time of about 1.6 h. Thus, a rate-limiting step(s) in secretion occurs subsequent to translocation and N glycosylation of the t-PA polypeptide. Treatment of Sf9 cells with tunicamycin, but not with inhibitors of oligosaccharide processing, prevented the appearance of t-PA in the extracellular medium. This suggests that N glycosylation per se, but not processing of the N-linked oligosaccharides, is required directly or indirectly in baculovirus-infected Sf9 cells for the secretion of t-PA. Finally, the relative efficiency of secretion decreased dramatically with time of infection, suggesting that the Sf9 host cell secretory pathway is compromised during the later stages of baculovirus infection.

Production of human beta interferon in insect cells infected with a baculovirus expression vector.

Autographa californica nuclear polyhedrosis virus (AcNPV) was used as an expression vector for human beta interferon. By using specially constructed plasmids, the protein-coding sequences for interferon were linked to the AcNPV promoter for the gene encoding for polyhedrin, the major occlusion protein. The interferon gene was inserted at various locations relative to the AcNPV polyhedrin transcriptional and translational signals, and the interferon-polyhedrin hybrid genes were transferred to infectious AcNPV expression vectors. Biologically active interferon was produced, and greater than 95% was secreted from infected insect cells. A maximum of ca. 5 X 10(6) U of interferon activity was produced by 10(6) infected cells. These results demonstrate that AcNPV should be suitable for use as a eucaryotic expression vector for the production of products from cloned genes.

Production of human c-myc protein in insect cells infected with a baculovirus expression vector.

A cDNA fragment coding for human c-myc was inserted into the genome of the baculovirus Autographa californica nuclear polyhedrosis virus adjacent to the strong polyhedrin promoter. Insect cells infected with the recombinant virus produced significant amounts of c-myc protein, which constituted the major phosphoprotein component in these cells. By immunoprecipitation and immunoblot analysis, two proteins of 61 and 64 kilodaltons were detected with c-myc-specific antisera. The insect-derived proteins were compared with recombinant human c-myc-encoded proteins synthesized in Escherichia coli and Saccharomyces cerevisiae cells. The c-myc gene product was found predominantly in the nucleus by subcellular fractionation of infected insect cells.

Optical guiding of aerosol droplets.

We characterize the ability of Gaussian and Bessel beams to guide water, ethanol and dodecane aerosol droplets. Droplets produced from a nebuliser source are trapped using radiation pressure and then by varying the beam power are controllably guided in a vertical direction. The use of a zeroth-order Bessel beam, which has a non-diffracting thin core, is shown to improve guiding distances over a comparable Gaussian beam by more than three times with guiding distances of up to 2.75mm for dodecane droplets. We discuss the applications for this work in the context of tools for optically manipulating airborne particles.

Polyhedrin initiator codon altered to AUU yields unexpected fusion protein from a baculovirus vector.

A recombinant baculovirus expression vector was constructed to express the core (capsid) protein of the hepatitis B virus. Along with the expected 21-kDa polypeptide, a second 24-kDa protein was observed. Immunoprecipitation and immunoblotting using a rabbit polyclonal anticore antiserum demonstrated that the two proteins were related. The core gene originally was cloned in-frame with the polyhedrin initiator codon that had been altered to AUU as a means of preventing fusion protein formation. A transient expression assay revealed expression of the 24-kDa protein was prevented if a frame-shift mutation was created upstream of the HBV core translation start site. These results suggest that the 24-kDa protein was the result of an unexpectedly high level of translation initiation at the AUU codon that gave rise to a polyhedrin-HBV core fusion protein. The 24-kDa core protein was shown to be a polyhedrin fusion protein by immunoblotting with an antipolyhedrin antiserum, and initiation at the AUU was demonstrated by amino terminal protein sequencing. Methods to prevent undesired fusion protein expression using this or similar vectors are discussed.

Use of early baculovirus promoters for continuous expression and efficient processing of foreign gene products in stably transformed lepidopteran cells.

Baculoviruses are currently used as vectors for the transient high-level expression of foreign gene products in insect cells. In this study, we demonstrate that baculoviruses can also be made to continuously express a foreign gene product by using the promoter from IE1, an immediate early viral gene, to produce stably-transformed insect cells. This approach gave levels of foreign gene expression lower than those usually obtained with the lytic baculovirus expression vector system. Expression, however, was continuous and stable, and a complex human glycoprotein (tissue plasminogen activator) was processed more efficiently. We conclude that stable transformation is a feasible approach for baculovirus-mediated foreign gene expression in lepidopteran cells, particularly for products that are relatively poorly-expressed and/or processed in lytically infected cells.

Apparent in vivo pathway of granulosis virus invasion and infection.

The invasion and ensuing replication of an insect granulosis virus in Trichoplusia ni is described.

Comparative studies of baculovirus granulins and polyhedrins.

Granulins and polyhedrins from five baculoviruses exhibit similar chemical and physical properties. Although similarities are demonstrated, it has been shown that each of the proteins is different and apparently specific to a given virus. The granulins and polyhedrins exhibit a major polypeptide component of an estimated molecular weight of 28,000. Alkaline protease activity has been detected in each preparation. N-terminal analyses reflect differences between granulins and polyhedrins studied: granulosis virus = Asx, and nuclear polyhedrosis virus = Glx. Two-dimensional high-voltage electrophoresis of highly purified granulin and polyhedrin preparations reveals relatedness as well as differences among the proteins as assessed by electrophoretic migration patterns.

Analysis of baculovirus genomes with restriction endonucleases.

The viral DNAs from nine wild-type insect baculoviruses have been isolated and the EcoR-1 restriction endonuclease fragment patterns compared. Genomic heterogeneity could be detected in the DNA restriction patterns of four of these wild-type baculoviruses. Three infectious virus forms (two that are occluded in the nucleus and an extracellular virus that has budded from the plasma membrane of infected cells) of a nuclear polyhedrosis virus with multiple nucleocapsids per envelope (MNPV) from the lepidopteran insect, Autographa californica are shown to be phenotypically distinct by comparison of viral structural polypeptides by polyacrylamide gel electrophoresis and autoradiography of L[35S]methio-nine-labeled virus proteins. The three phenotypic forms were cloned by successive plaque purification and eight distinct variants were identified from 11 plaque-purified viruses by genotypec analysis with EcoR-1 and HindIII restriction endonuclease. Isolation of variants from the three phenotypic forms has shown that each of the infectious forms is heterogeneous and that no segregation of genotypes among the three forms was evident. The characteristic restriction fragment patterns of several variants were maintained upon multiple passage in cell culture.

Restriction Maps of Five Autographa californica MNPV Variants, Trichoplusia ni MNPV, and Galleria mellonella MNPV DNAs with Endonucleases SmaI, KpnI, BamHI, SacI, XhoI, and EcoRI.

The restriction sites of Autographa californica nuclear polyhedrosis virus (AcMNPV) E2 DNA were mapped for the endonucleases SmaI, KpnI, BamHI, SacI, XhoI, and EcoRI. The restriction maps of four other AcMNPV variants, Trichoplusia ni (TnMNPV), and Galleria mellonella (GmMNPV) genomes were determined and compared to the endonuclease cleavage maps of AcMNPV E2 DNA. The viral structural polypeptides of AcMNPV variants S3, E2, S1, M3, and R9 were the same when analyzed by polyacrylamide gel electrophoresis. The major structural polypeptides of GmMNPV and TnMNPV had the same pattern in polyacrylamide gels as did AcMNPV structural polypeptides. GmMNPV and TnMNPV had several minor structural protein differences as compared with AcMNPV. AcMNPV variants, TnMNPV, and GmMNPV were distinct but with very similar genomes and protein structures.

Sequence comparison of cellular and viral copies of host cell DNA insertions found in Autographa californica nuclear polyhedrosis virus.

The nucleotide sequence and structural characteristics of two nonhomologous host DNA insertions of Spodoptera frugiperda (fall armyworm) origin isolated from few polyhedra mutants of the baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV) have been determined. Neither of the host insertions contain long open reading frames suggesting that cellular genes were not introduced into the viral genome. One of the host DNA insertions, IFP1.6, terminated in short imperfect inverted repeats flanked by a duplication of the target sequence, TTAA. Analysis of three cellular copies of this host insertion isolated from a lambda genomic library of S. frugiperda DNA revealed the termini to be highly conserved and also flanked by the same TTAA sequence. IFP1.6 was shown to share homology with a putative host insertion described in the genome of a baculovirus exhibiting wild-type plaque morphology. The second of the host insertions, IFP2.2, had a structure unique among host insertions described in baculoviruses. It lacks terminal repeats but is flanked by duplications of the 8-bp target site sequence. The cellular copy of this insertion was conserved in comparison to the viral copy and was also flanked by a direct 8-bp repeat. This is the first report of the analysis of cellular copies of host DNA insertions frequently associated with baculovirus FP mutants.

Comparisons of host cell DNA insertions and altered transcription at the site of insertions in few polyhedra bacilovirus mutants.

Few polyhedgra (FP) mutants of Autographa californica nuclear polyhedrosis virus (AcNPV) and the closely related strain Galleria mellonella (Gm)NPV have been reported which contain Trichoplusia ni host cell DNA sequences inserted into the viral genome between map units 35.0 and 37.7. New FP mutants are described with alterations of the HindIII-I restriction enzyme fragment (33.8 to 37.7 map units) of AcNPV, either deletions of viral DNA sequences or insertions of spodoptera frugiperda host cell DNA sequences. S. frugiperda DNA insertions from FP mutants were compared to T. ni host DNA insertions from FP mutants previously isolated (M.J. Fraser, G.E. Smith, and M.D. Summers (1983) J. Virol. 47, 287-300). Two host cell DNA sequences isolated from FP mutants, one of T. ni origin and one from S. frugiperda DNA, were transcribed in infected cells. Deletions of viral DNA sequences and insertions of host DNA sequences produce altered transcripts at the site of mutation as determined by both Northern and S1 nuclease analysis. Cell-free translation of cRNAs transcribed from wild-type viral DNA revealed an open reading frame coding for a 25-kDa protein at the site where host cell DNA insertions have been mapped. This was the same size as an infected-cell protein missing from most FP mutants examined.

Functional mapping of Autographa california nuclear polyhedrosis virus genes required for late gene expression.

A plasmid containing the bacterial chloramphenicol acetyltransferase (CAT) gene under the control of an Autographa california nuclear polyhedrosis virus (AcNPV) late gene promoter was constructed. This plasmid (pL2cat) also contained the AcNPV hr5 enhancer element. Transient-expression assay experiments indicated that the late promoter was active in Spodoptera frugiperda cells cotransfected with pL2cat and AcNPV DNA but not when pL2cat was transfected alone. Low levels of CAT activity were observed in cells cotransfected with pL2cat and pIE-1 DNAs. However, CAT activity was not induced in a similar plasmid which lacked the cis-linked enhancer element, indicating that the enhancer was required for expression of the late gene. Cotransfection mapping of pPstI clones of AcNPV DNA indicated that the pPstI-G clone of viral DNA contained a factor which further stimulated late gene expression 3- to 10-fold. Transient-expression assay analysis of subclones of pPstI-G localized the trans-active factor to a 3.0-kilobase XbaI fragment. The nucleotide sequence of this fragment was determined and found to contain three potential open reading frames. A computer-assisted search of a protein database revealed no closely related proteins. One of the predicted amino acid sequences contained potential metal-binding domains similar to those found in nucleic acid-binding proteins. Subcloning and subsequent CAT assay indicated that two of the open reading frames were required for the activation of pL2cat. Nuclease S1 mapping of infected and transfected RNAs indicated that the two open reading frames were transcribed as delayed-early genes. Quantitative nuclease S1 analysis and differential DNA digestion of recovered plasmids indicated that the activation of pL2cat was not due to an increase in steady-state levels of mRNA replication of the viral DNA.

Signals important for high-level expression of foreign genes in Autographa californica nuclear polyhedrosis virus expression vectors.

The transcriptional and translational signals required for efficient expression of the chloramphenicol acetyltransferase, beta-galactosidase, and tissue plasminogen activator genes, under the control of the polyhedrin promoter in Spodoptera frugiperda cells infected with Autographa californica nuclear polyhedrosis virus, were investigated by SDS-PAGE and RNA dot blot analysis. The recombinant baculoviruses all contained alterations in the leader sequence or 5' proximal coding region of the polyhedrin gene. Highest levels of foreign proteins and polyhedrin-linked mRNAs were observed when portions of the coding sequence of the polyhedrin gene were fused in phase with the foreign gene. Recombinant viruses in which the foreign gene was inserted upstream from the polyhedrin ATG start codon expressed nonfused products but at lower levels than contructs which produced fusion proteins. A corresponding decrease in the levels of mRNAs produced by such constructs was also observed. Some constructs in which the foreign gene was inserted out of phase downstream from the polyhedrin start codon expressed nonfused protein products at low levels but produced polyhedrin-linked mRNA at levels comparable to vectors which produced protein fusions. These data suggest that reinitiation of translation can take place at AUG start codons a short distance downstream from the primary polyhedrin start codon. These results indicate that sequences immediately upstream from the polyhedrin start codon are important for regulation of transcription and that additional sequences near the AUG start codon can have a dramatic influence on the levels of translation observed.

Identification and comparison of Campoletis sonorensis virus transcripts expressed from four genomic segments in the insect hosts Campoletis sonorensis and Heliothis virescens.

The Campoletis sonorensis virus (CsV; Polydnaviridae) genome consists of at least 28 closed circular superhelical (SH) DNAs. In this study we used complete clones of four SH DNAs to analyze viral transcription both in the adult parasitic wasp host Campoletis sonorensis (Ichneumonidae) and in the lepidopteran host, Heliothis virescens (Noctuidae). CsV genes are expressed in parasitized H. virescens, but no viral transcripts had been characterized from C. sonorensis until this study. The clones of the SH DNAs B, H, M, and O1 were used to probe Northern blots of poly(A)+ RNA isolated from C. sonorensis reproductive tissue and from parasitized H. virescens larvae. All four SH DNAs hybridized to viral transcripts. SH-H,-M, and -O1 hybridized to messages expressed in both hosts. SH-B and -M hybridized to transcripts that were detected only in either C. sonorensis reproductive tissue or parasitized H. virescens larvae. These results suggest that some CsV genes are expressed in a host-specific manner. In a previous study we identified a family of imperfectly conserved tandemly repeated 540-bp repeat elements on SH-B,-H and -O1 (D. A. Theilmann and M. D. Summers, 1987 J. Virol. 61; 2589-2598). Hybridization of the 540-bp repeat regions to Northern blots showed that they were all homologous to viral transcripts. A cDNA clone of a mRNA that is transcribed from the 540-bp repeat region of SH-B was isolated from a lambda gt 10 library and completely sequenced. The sequence data revealed that the 540-bp repeat element was contained within the open reading frame of this gene. These results indicate that transcribed sequences homologous to the 540-bp repeat elements represent a second gene family to be identified within the CsV genome.

Expression of Sindbis virus 26S cDNA in Spodoptera frugiperda (Sf9) cells, using a baculovirus expression vector.

To study protein processing in an insect Spodoptera frugiperda (fall armyworm; Sf9) cell line, a 26S cDNA encoding the sequence of Sindbis virus structural proteins (capsid protein, of 30 kilodaltons [kDa]; p62 [the precursor of E3 and E2], of 62 kDa; a 6-kDa peptide; and the E1 protein, of 56 kDa) was inserted into the genome of Autographa californica nuclear polyhedrosis virus (AcNPV) adjacent to the polyhedrin promoter. By immunoblot analysis with antisera directed against whole Sindbis virus and the individual structural proteins (capsid, E2, and E1), we have shown that polypeptides similar in size and antigenicity to those synthesized in Sindbis virus-infected BHK cells are expressed in Sf9 cells infected with the recombinant baculovirus Ac373-SV26. By pulse-chase labeling in the presence or absence of tunicamycin, by endo-beta-N-acetylglucosaminidase H (endo-H) treatment of the recombinant glycoproteins, and by N-terminal sequence analysis of the E1 envelope glycoprotein, we have further shown that the 26S transcription translation unit of Sindbis virus, although normally encoded by nonnuclear RNA, is expressed and proteolytically cleaved similarly, if not identically, in Sf9 cells as compared with BHK cells when a baculovirus expression vector is used.

Location and nucleotide sequence of the 25K protein missing from baculovirus few polyhedra (FP) mutants.

Wild-type and few polyhedra (FP) mutants of the baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV) were studied to identify and sequence the gene encoding the 25-kDa (25K) protein normally present in AcMNPV-infected Spodoptera frugiperda cells but which is often missing from FP mutant-infected cells. Our previous study had mapped two overlapping late transcripts to the insertion site of host cell DNA within the HindIII-I fragment (33.8 to 37.7 map units) of wild-type AcMNPV. An FP mutant, AcFP875-2, had a 1.6-kbp insertion of S. frugiperda DNA near the 5' end of these transcripts which by S1 analysis were shown to initiate within the host cell sequence. Primer extension analysis revealed that the transcription start for this gene in wild-type virus occurred within a conserved 12-base sequence found near the transcription start sites of several baculovirus late and hyper-expressed genes. A similar 12-base sequence was found at the transcription start site within this 1.6-kbp pair host cell DNA sequence in AcFP875-2. mRNAs from wild-type virus-infected cells were hybridization-selected using a 542-bp SalI subfragment of the 3.2-kbp EcoRI-HindIII fragment (35.0 to 37.7 map units). These mRNAs directed the synthesis of a 25K protein which in size was identical to the 25K protein in wild-type virus-infected cells and the translation product of a 1.15-kb cRNA transcribed from a RsaI fragment (36.4 to 37.4 map units). Comparison of gel band patterns following partial proteolysis of the translation product of the 1.15 cRNA and the 25K protein from wild-type virus-infected cells revealed that the two proteins were closely related if not identical. Nucleotide sequence analysis within this EcoRI-HindIII fragment revealed an open reading frame which encodes a 25K protein. Insertion of the Escherichia coli lacZ gene encoding the beta-galactosidase enzyme into the transcribed portion of this EcoRI-HindIII fragment yielded a recombinant virus which lacked a 25K protein and exhibited an altered (FP) plaque phenotype.

Autographa californica nuclear polyhedrosis virus, PDV, and ECV viral envelopes and nucleocapsids: structural proteins, antigens, lipid and fatty acid profiles.

Autographa californica nuclear polyhedrosis virus (AcMNPV) infection results in the production of two types of infectious, enveloped viruses. As both of these viral forms play significantly different roles in the virus life cycle, the different functional characteristics in the roles of the virus may be explained, in part, by the protein and lipid composition and source of the viral envelopes. Both viruses utilize different maturation and envelopment strategies: Extracellular virus (ECV) obtains an envelope by budding from the host cell plasma membrane, while the envelope of polyhedra-derived virus (PDV) is obtained within the nucleus of the host cell. There is compelling evidence for differences between ECV and PDV structural proteins; however, no previous study directly compares ECV and PDV purified from the same source and little data are available on the protein and lipid composition of the viral envelopes. This study begins the systematic comparison of ECV, PDV, and their envelopes to target proteins for use as probes to study the molecular and biochemical basis of viral envelopment within the nucleus. AcMNPV ECV and PDV were isolated from infected Spodoptera frugiperda cells and fractionated into their respective envelope and nucleocapsid fractions. The structural protein, glycoprotein, and phosphoprotein composition of ECV, PDV, and their envelope and nucleocapsid fractions are analyzed and compared, and antigens of ECV and PDV viral envelope are identified. A number of structural proteins are different between ECV and PDV. ECV is enriched for proteins at 67, 45, and 35 kDa, while proteins at 89, 70, 60, 50, and 25 kDa are enriched in PDV. At least two proteins, PDV-E66 and PDV-E43, are identified to be specific for the PDV envelope. There are more N-glycosylated proteins in ECV than in PDV, with ECV-specific proteins found at 137, 128, 89, 45, and 40 kDa. PDV glycoproteins are 70, 53, 49, 42, 40, and 31 kDa. Most phosphoproteins of both ECV and PDV are predominantly found in the viral envelopes. The predominant phosphoprotein of ECV is 85 kDa, whereas PDV major phosphoprotein is 36 kDa. This study presents the first report of the phospholipid and fatty acid content of ECV and PDV viral envelopes. The major phospholipid of ECV is phosphatidylserine (50%), while phosphatidylcholine and phosphatidylethanolamine are the major phospholipids of PDV (39 and 30%, respectively). Since PDV is enveloped within the nucleus of the host cell, the PDV phospholipid composition is compared with the phospholipid composition of purified S. frugiperda (Sf9) nuclei and this analysis demonstrates significant differences between these two membrane systems.