The structural properties and identification of insect viruses

Temporal analysis of the honey bee microbiome reveals four novel viruses and seasonal prevalence of known viruses, Nosema, and Crithidia

Honey bees (Apis mellifera) play a critical role in global food production as pollinators of numerous crops. Recently, honey bee populations in the United States, Canada, and Europe have suffered an unexplained increase in annual losses due to a phenomenon known as Colony Collapse Disorder (CCD). Epidemiological analysis of CCD is confounded by a relative dearth of bee pathogen field studies. To identify what constitutes an abnormal pathophysiological condition in a honey bee colony, it is critical to have characterized the spectrum of exogenous infectious agents in healthy hives over time. We conducted a prospective study of a large scale migratory bee keeping operation using high-frequency sampling paired with comprehensive molecular detection methods, including a custom microarray, qPCR, and ultra deep sequencing. We established seasonal incidence and abundance of known viruses, Nosema sp., Crithidia mellificae, and bacteria. Ultra deep sequence analysis further identified four novel RNA viruses, two of which were the most abundant observed components of the honey bee microbiome (∼10(11) viruses per honey bee). Our results demonstrate episodic viral incidence and distinct pathogen patterns between summer and winter time-points. Peak infection of common honey bee viruses and Nosema occurred in the summer, whereas levels of the trypanosomatid Crithidia mellificae and Lake Sinai virus 2, a novel virus, peaked in January.

Bacterial, viral, and fungal insecticides

Microorganisms that are pathogenic to insects provide a wealth of biological material that can be exploited by humans to control insect pests. Innovative applications of a few such entomopathogens are found throughout the world, but widespread commercial production of microbial insecticides awaits further studies of the biology, ecology, and pathogenicity of the agents. Genetic engineering techniques may be used to increase the virulence of these microorganisms, as well as to make them more tolerant of physical and chemical conditions and perhaps to broaden their host ranges. The use of microbial insecticides could decrease our dependence on chemical pesticides.

Orientation of the Genome of Autographa californica Nuclear Polyhedrosis Virus: a Proposal

The nuclear polyhedrosis virus of the alfalfa looper Autographa californica contains a double-stranded, circular DNA genome. Fourteen scientists agreed to accept an orientation of this circular genome with respect to a physical map of the restriction endonuclease cleavage sites.

Location of Homologous DNA Sequences Interspersed at Five Regions in the Baculovirus AcMNPV Genome

An examination of Autographa californica nuclear polyhedrosis virus DNA revealed the presence of five interspersed regions, rich in EcoRI restriction sites, which shared homologous sequences. These homologous regions (hr), designated hr(1) to hr(5), occur at or near the following EcoRI fragment junctions: hr(1)EcoRI-B-EcoRI-I (0.0 map units); hr(2), EcoRI-A-EcoRI-J (19.8 map units); hr(3), EcoRI-C-EcoRI-G (52.9 map units); hr(4), EcoRI-Q-EcoRI-L (69.8 map units); and hr(5), EcoRI-S-EcoRI-X (88.0 map units). Four of these regions were identified, by cross-blot hybridization of HindIII-restricted A. californica nuclear polyhedrosis virus DNA, to be within the HindIII-A/B, -F, -L, and -Q fragments. The location of these regions and the identification of a fifth homologous region were confirmed, and their characterization was facilitated, by using two plasmids with HindIII-L or -Q fragment insertions, which contained the homologous regions hr(2) and hr(5), respectively. The sizes of the homologous regions were about 800 base pairs for hr(2), 500 base pairs for hr(5), and less than 500 base pairs for hr(1), hr(3), and hr(4). A set of small EcoRI fragments (EcoRI minifragments) which ranged in size from 225 to 73 base pairs were detected in A. californica nuclear polyhedrosis virus DNA and HindIII-L and -Q fragments by polyacrylamide gel analysis. Some of the minifragments in viral DNA were present in extramolar amounts and corresponded in size to some of the minifragments present in HindIII-L and -Q. Clones of some of the EcoRI minifragments were used as probes in hybridizations to digests of viral DNA and of HindIII-L and -Q. The hybridization data, obtained under various levels of stringency, suggested that there was a degree of mismatching between the sequences which were responsible for the homology.

Insect viruses as control agents

Virus diseases have been reported from more than 800 species of insects and mites. Isolates of the baculovirus and cytoplasmic polyhedrosis virus groups have biological properties which should lead to their successful use as microbial control agents in integrated pest management programmes. These viruses infect the larval stages of many lepidopterous and hymenopterous pests, producing a chronic or lethal infection and the release of large quantities of relatively stable infective inclusion bodies (IBs). The IBs serve as the means by which the viruses are transmitted and persist outside the host. Younger larvae are more susceptible to infection than older stages, and this difference influences the timing of application and doses of virus needed for practical pest control. The high degree of host specificity of many isolates reduces their potential ecological hazard but also limits their use, particularly on crops where a complex of pests is established. Environmental persistence is also a limiting factor as virus is rapidly inactivated by ultra-violet light even when contained within IBs. The viruses persist for longer periods when transmitted within the host population, a feature of virus infections restricted to the insect gut.

The practical use of insect viruses in horticulture and agriculture does not utilize their full epizootic potential, but takes advantage of their high pathogenicity and specificity. The baculoviruses of codling moth, andHeliothisspp. provide satisfactory pest control, but for their most cost-effective use it is important to determine the minimum dosage rates of virus required. It is encouraging that studies of the virus control ofPierisspp. have suggested that control achieved by the insecticidal use of a virus can be closely predicted from information on dosage-mortality responses, larval feeding rates and virus persistence. The stability of forest and grassland, and their high economic thresholds makes them ideal candidates for longer-term control. Viruses of the coconut rhinoceros beetle and european spruce sawfly provide examples of classical biological control where the viruses persist for long periods, are efficiently transmitted and act as natural regulators of their hosts. Virus control of pasture, and some forest, pests may be possible by manipulating enzootic viruses without the need for direct control measures. More frequently insecticidal applications are needed, providing control of limited duration which requires periodic ‘topping-up’.

Few viruses are commercially-available; their selectivity and often small potential market, may limit industrial interest. However, improvements in virus production, formulation and a better understanding of virus epizootiology should lead to an increasing role for this group of insect pathogens in biological control.

Comparison of sequence diversity in several cytoplasmic polyhedrosis viruses

Sequence homology among several different cytoplasmic polyhedrosis virus (CPV) types and the human reovirus (type 1) was examined by Northern blot analysis and S, nuclease analysis, using random-primed cDNA probes synthesized from total genomic RNA. The results show no homology among the CPV type 1, Bombyx mori CPV, type 5, Orgyia pseudotsugata CPV, type 8, Manduca sexta CPV and the human reovirus (type 1). However, there was significant homology among three type 5 CPVs, O. pseudotsugata CPV, Euxoa scandens CPV, and Heliothis armigera CPV. The O. pseudotsugata CPV and E. scandens CPV were 43-44% homologous while each was 6-13% homologous with the H. armigera CPVusing stringent conditions of hybridization.

Induction of a nonoccluded baculovirus persistently infecting Heliothis zea cells by Heliothis armigera and Trichoplusia ni nuclear polyhedrosis viruses

A nonoccluded singly enveloped baculovirus (baculovirus X) persistently infects Heliothis zea (IMC-HZ-1) cells in culture. Singly enveloped nuclear polyhedrosis viruses from H. zea and Heliothis armigera, and multiply enveloped nuclear polyhedrosis viruses from Trichoplusia ni, Spodoptera frugiperda, and Spodoptera littoralis were all found to induce baculovirus X. Experiments are reported which use metabolic inhibitors and inactivated inducing virus to show that it is probable that a structural component of the virus, most likely a protein, is responsible for inducing baculovirus X. The persistent virus is induced to replicate by uv-inactivated virus but not by heat-inactivated inducing virus. The virus is not induced to replicate by a number of metabolic inhibitors in the absence of an inducing virus. Inhibition of transcription and translation prevents the induction of the persistent virus by an inducing virus. Inhibition of DNA replication has no effect on the induction of the virus. This suggests that the persistent virus genome is present in abundance in all cells.

Purification and characterization of a virus from the aphid Rhopalosiphum padi

A 27-nm icosahedral virus was purified from the oat bird cherry aphid, Rhopalosiphum padi (L.). The virus had an s(20,w) of 162 +/- 2 S, and bouyant densities of 1.37 in CsCl and 1.35 in Cs2SO4. It contained one ssRNA of 31 +/- 2 S and three major proteins. The relationship of the R. padi virus to other small RNA invertebrate viruses is unclear.

Lipofectin increases the specific activity of cypovirus particles for cultured insect cells

Cytoplasmic polyhedrosis viruses (CPV) are classified as 14 distinct species (electropherotypes) within the genus Cypovirus, family Reoviridae. Cypovirus research has been limited by a lack of appropriate cell culture systems (for each of these virus species) in which the majority of cells can become productively infected. Lipofection increased the infection rate of Lymantria dispar 652 cells, by virus particles (derived from polyhedra) of Orgyia pseudosugata type 5 cypovirus (Op-5 CPV), from 3 to 44%. Lipofection also significantly increased the percentage of Trichoplusia ni 368 cells infected with the same virus (from < 1 to approximately 7%). The spread of cypovirus infection between cells was either very slow or insignificant, and infected cells appeared to remain viable for long periods. Virus infection was detected by the observation of polyhedra formation in individual cells and it was therefore possible to develop a simple quantitative assay system to measure virus titre (TCID50). Cryo-electron microscopy showed that cypovirus particles formed a complex with the lipid, involving their envelopment within the liposome membrane. It was concluded that the increased infectivity of the virus by lipofection was due to a more efficient cell entry mechanism, probably involving fusion between liposome and cell membranes.

Identification of a novel Lymantria dispar nucleopolyhedrovirus mutant that exhibits abnormal polyhedron formation and virion occlusion

In previous studies on the formation of Lymantria dispar nuclear polyhedrosis virus (LdMNPV) few polyhedra (FP) mutants, several polyhedron formation mutants (PFM) were identified that appeared to be unique. These viral mutants are being characterized to investigate the processes of polyhedron formation and virion occlusion. LdMNPV isolate PFM-1 is one of these mutants, and is described in this report. Genetic techniques were used to determine if isolate PFM-1 contained a mutation in the polyhedrin or 25K FP gene. Wild-type viruses were recovered after coinfection of Ld652Y cells with isolate PFM-1 and a FP mutant, and with isolates PFM-1 and PFM-C (isolate PFM-C contains a mutation in the polyhedrin gene). These viruses were analyzed by genomic restriction endonuclease digestion and found to be chimeras of the original PFMs used in the coinfections. Marker rescue studies mapped the mutation in isolate PFM-1 to a genomic region that does not include the polyhedrin or 25K FP genes. Isolate PFM-1 produced approximately 14-fold fewer polyhedra than LdMNPV isolate A21-MPV, an isolate that produces wild-type levels of polyhedra, and approximately 2-fold more polyhedra compared to the FP isolate 122-2. Polyhedra generated by isolate PFM-1 were normal in size and shape but contained very few viral nucleocapsids. The same amount of budded virus (BV) was released from cells infected with isolates PFM-1 and A21-MPV. In contrast, isolate 122-2 yielded significantly more BV than isolates PFM-1 and A21-MPV.

Characterization of a granulosis virus from the castor semilooper, Achaea janata L

The granulosis virus isolated from Achaea janata is composed of capsules (463 +/- 25 x 280 +/- 22 nm) which contain single virus particles. The virus particles (274 +/- 9 x 95 +/- 4 nm) contain nucleocapsids (297 +/- 7 x 52 +/- 2 nm) within an envelope. The empty capsids measured 265 +/- 9 x 63 +/- 3 nm. SDS-PAGE electrophoresis was carried out and the granulin polypeptide (28.9 +/- 0.5 kDa) was found to contain two other associated polypeptides of molecular weight 58.2 +/- 2.3 and 55.2 +/- 1.3 kDa, respectively. Protein gel electrophoresis of granulin gave degradation products from 27.2 to 15.4 kDa, when protease associated with capsules was not inhibited. The virus particles were found to contain 16 polypeptides with molecular weights ranging from 106.4 +/- 2.1 to 15. 5 +/- 0.8 kDa and 12 of these polypeptides were contained in the nucleocapsids. The major polypeptide of the capsids had molecular weight of 34.9 +/- 0.3 kDa. Restriction profiles of viral DNA with seven enzymes were obtained and the average molecular weight was found to be approximately 92 +/- 7 kb. Southern hybridization of the restriction profiles of the viral DNA with SalI fragment from pUCTnGV (containing granulin gene) was performed and hybridization was found on single discrete fragments with molecular weights ranging from 12.0 to 2.7 kb. The GC content of AjGV DNA was found to be 65 +/- 1% and the genome size as determined from reassociation kinetics was 92 kb.

Characterization of the replication cycle of the Lymantria dispar nuclear polyhedrosis virus

The life cycle of the Lymantria dispar nuclear polyhedrosis virus (LdMNPV) was characterized through analysis of budded virus (BV) release, the temporal formation of polyhedra, the temporal transcription pattern of representative early, late, and hyper-expressed late genes, and the onset of DNA replication in the Ld652Y cell line. Transcripts from the LdMNPV immediate early gene G22 were detected 4 h post infection (h p.i.). The late and hyper-expressed late p39 capsid and polyhedrin genes were initially transcribed at approximately 20 and 24 h p.i., respectively. Viral DNA replication initiated at approximately 18-20 h p.i. Budded virus was released from infected cells between 24 and 36 h p.i., and polyhedra were first detected at approximately 48 h p.i.

Physical mapping of the genomic DNA of the Oryctes rhinoceros baculovirus, KI

A non-occluded baculovirus, OBV-KI has been isolated from the insect pest, Oryctes rhinoceros. The viral genome is estimated to be 123 kb, with a G + C content of 43 mol% and no detectible methylated bases. A restriction map of the OBV-KI genome for BamHI, EcoRI, HindIII, PstI, SalI and XbaI has been constructed.

Temporal analysis and spatial mapping of Lymantria dispar nuclear polyhedrosis virus transcripts and in vitro translation polypeptides

Genomic expression of the Lymantria dispar multinucleocapsid nuclear polyhedrosis virus (LdMNPV) was studied. Viral specific transcripts expressed in cell culture at various times from 2 through 72 h postinfection were identified and their genomic origins mapped through Northern analysis. Sixty-five distinct transcripts were identified in this analysis. Most viral transcripts were expressed late in infection, and originated from throughout the viral genome. Viral polypeptides expressed in infected 652Y cells were labeled with [35S]methionine and identified by autoradiography after separation by SDS polyacrylamide gel electrophoresis. Viral protein synthesis was found to occur in a sequential manner. Four proteins were identified in the early phase of viral replication (4-12 h p.i.), 24 proteins in the intermediate phase (12-24 h p.i.), and 5 proteins during the late phase (greater than 24 h p.i.). Cytoplasmic RNAs were isolated from LdMNPV infected cells at 16, 24, and 48 h p.i., and used for hybrid selections with overlapping DNA fragments that covered the entire LdMNPV genome. The selected RNAs were translated in vitro, and 61 distinct viral polypeptides were identified and their genomic origins mapped. Temporal and spatial transcription and translation maps of the LdMNPV genome were generated with these data, and the expression pattern of the LdMNPV genome was compared to that of the Autographa californica nuclear polyhedrosis virus.

Tissue-specific expression of silkmoth chorion genes in vivo using Bombyx mori nuclear polyhedrosis virus as a transducing vector

A pair of silkmoth chorion chromosomal genes, HcA.12-HcB.12, was inserted into a baculovirus transfer vector, pBmp2, derived from the nuclear polyhedrosis virus of Bombyx mori. This vector, which permits the insertion of foreign genetic material in the vicinity of a mutationally inactivated polyhedrin gene, was used to acquire the corresponding recombinant virus. Injection of mutant silkmoth pupae that lack all Hc chorion genes with the recombinant virus resulted in the infection of all internal organs including follicular tissue. Analysis of RNA from infected tissues has demonstrated that the two chorion genes present in the viral genome are correctly transcribed under the control of their own promoter in follicular cells, the tissue in which chorion genes are normally expressed. The chorion primary transcripts are also correctly processed in the infected follicular cells and yield mature mRNAs indistinguishable from authentic chorion mRNAs present in wild-type follicles. These results demonstrate that recombinant nuclear polyhedrosis viruses can be used as transducing vectors for introducing genetic material of host origin into the cells of the organism and that the transduced genes are transiently expressed in a tissue-specific manner under the control of their resident regulatory sequences. Thus we show the in vivo expression of cloned genes under cellular promoter control in an insect other than Drosophila melanogaster. The approach should be applicable to all insect systems that are subject to nuclear polyhedrosis virus infection.

Comparison of a DNA-DNA dot-blot hybridisation assay with light microscopy and radioimmunoassay for the detection of a nuclear polyhedrosis virus

A dot-blot hybridisation assay was developed for the detection of a nuclear polyhedrosis virus (NPV) and was compared to light microscopy and radioimmunoassay (RIA). Using cloned NPV DNA labelled with 32P as a probe, a number of hybridisation assay procedures was examined. The assay was found to be more sensitive than differential staining, phase-contrast microscopy, or indirect solid-phase RIA with as few as 20 occlusion bodies (150 pg DNA) being detected. Samples do not require prior purification or DNA extraction. The assay was shown to be specific for NPV and has the potential to detect and discriminate between strains of the virus. With little modification the assay may be used to detect other insect viruses.

Polyhedrin gene of Bombyx mori nuclear polyhedrosis virus

A portion of the genome of the nuclear polyhedrosis virus of Bombyx mori has been cloned. This part of the viral genome contains the gene encoding the viral occlusion body protein, polyhedrin. The polyhedrin gene has been sequenced in its entirety together with some of its 5' and 3' flanking sequences. The primary structure of polyhedrin predicted from the nucleotide sequence of the gene was found to be somewhat different from the one reported previously for the authentic protein (E. A. Kozlov, T. L. Levitina, N. M. Gusak, and S. B. Serebryani, Bioorg. Khim., 7:1008-1015, 1981; S. B. Serebryani, T. L. Levitina, M. L. Kautsman, Y. L. Radavski, N. M. Gusak, M. N. Ovander, N. V. Sucharenko, and E. A. Kozlov, J. Invertebr. Pathol., 30:442-443, 1977). Comparison of the primary structures of the polyhedrin of the nuclear polyhedrosis virus of B. mori with that of Autographa californica suggests that considerable selective pressure has been exercised at the protein level during evolution. Nucleotide sequence comparisons of the two structural genes reveal that the coding sequences have diverged significantly through the accumulation of silent and replacement substitutions. In contrast, a remarkable degree of sequence conservation was found to exist in the domains corresponding to the 5' and 3' noncoding regions of the polyhedrin mRNAs.

Isolation of large and small plaque variants of the Autographa californica nuclear polyhedrosis virus. Brief report

Variants of the Autographa californica nuclear polyhedrosis virus which produce large (1.4 mm) or small (0.5 mm) plaques on Spodoptera littoralis cells have been isolated. Yields of extracellular virus and polyhedra by the large plaque variant were six-fold higher and 140-fold lower, respectively, than those obtained with the small plaque variant. However the two variants could not be distinguished when Spodoptera frugiperda cells were used.

Monoclonal antibodies to baculovirus structural proteins: determination of specificities by Western blot analysis

Conventional mouse hybridoma technology was utilized to produce a panel of monoclonal antibodies which reacted with baculovirus proteins. Using an enzyme-linked immunosorbent assay (ELISA), the hybridomas which were raised against polyhedrin from Autographa californica nuclear polyhedrosis virus (AcNPV) and Choristoeura fumiferana nuclear polyhedrosis virus (CfNPV) were found to cross-react differentially with polyhedrins and granulins from several species of baculoviruses. Hybridoma antibodies which reacted against the nonoccluded form (NOV) of AcNPV in an ELISA test expressed different specificities for the occluded form of the virus (OV), a mutant strain of AcNPV, and CfNPV. Four hybridoma clones produced antibody which neutralized the infectivity of AcNPV NOV. One hybridoma antibody reacted strongly with the uninfected Spodoptera frugiperda host cell line. Using Western blot analysis, it was shown that hybridoma antibodies against polyhedrin reacted differentially with the complete polypeptide and protease-generated fragments of polyhedrin. The polypeptide specificity of 19 of 28 hybridoma antibodies which reacted with OV and NOV of AcNPV was assigned using Western blot analysis.

Granulosis viruses, with emphasis on the GV of the Indian meal moth, Plodia interpunctella

The granulosis viruses and nuclear polyhedrosis viruses are being considered for use as biological insecticides for control of their insect hosts. Many of these insect species, which include some of the most serious pests of agriculture and forests, have become difficult to control because they have developed resistance to chemical insecticides. Several laboratory and field studies have demonstrated that the baculoviruses (GV and NPV) are promising alternatives to chemicals for the control of economically important insects. These viruses are highly virulent, selective, and stable, and the impact on the environment following their application is minimal. A decision concerning the application of baculoviruses to stored grain and field crops must be based upon a prudent consideration of the benefits to be obtained and the potential risks of their use. Such decisions should be made only after consideration of the physical, chemical, and biological properties of these viruses. In addition, methods must be developed for the unequivocal identification of these viruses, and their effects on nontarget species at the cellular and molecular levels must be investigated. This can best be accomplished if a sufficient body of knowledge regarding the molecular properties of these viruses and their infection process is accumulated by an extensive quantitative approach. Much of this knowledge is lacking because, prior to their consideration for use as insecticides, the baculoviruses appeared to have little medical or economic importance. As a result, interest in studying them was limited. It has become obvious that the molecular properties of these viruses must be investigated if full advantage is to be taken of using them as insect control agents, and if present and future problems concerning their use as insecticides are to be handled properly. Fundamental research on the biochemical and biophysical properties of baculoviruses has concentrated mainly on a variety of nuclear polyhedrosis viruses (Harrap, 1972a,b; Harrap et al., 1977; Summers and Smith, 1975a,b; Arif and Brown, 1975). Much of this progress can be attributed to tissue culture-host cell systems available for the NPVs. The in vitro host system(s) has allowed insect virologists to make phenomenal strides in understanding the cellular and molecular events of virus infection, and, in addition, to enter the era of biochemical sophistication in which animal virology is found at present.(ABSTRACT TRUNCATED AT 400 WORDS)

The proteins expressed by different isolates of Drosophila C virus

Isolates of Drosophila C virus (DCV) from Drosophila flies obtained in geographically different regions were adapted to growth in Drosophila tissue culture cells. The viruses, purified from tissue culture cells, were shown to be serologically related to one of the isolates ("O" from Ouarzazate, Morocco). Analysis of the structural proteins by polyacrylamide gel electrophoresis demonstrated differences between the isolates. Labelling intracellular proteins of infected Drosophila melanogaster cells with 35S-methionine at 28 degrees C demonstrated the presence of the virus structural proteins and their immediate precursors. Raising the temperature to 37 degrees C both before and during the pulse period inhibited the processing of the high molecular weight proteins and resulted in a greater "shut-off" of host cell proteins than viral induced proteins. This allowed the precursor proteins to be compared as well as the structural proteins of the different strains. It was possible to clearly distinguish differences between the isolates on the basis of the induced proteins, although limited proteolysis of corresponding proteins showed marked similarities. Hence it is possible to distinguish between different isolates of the "same" small RNA-virus of insects from geographically different regions.

N-Terminal polyhedrin sequences and occluded Baculovirus evolution

A phylogenetic tree for occluded baculoviruses was constructed based on the N-terminal amino acid sequence of occlusion body proteins from six baculoviruses including three lepidopteran nuclear polyhedrosis viruses (NPVs), [two unicapsid (Bombyx mori and Orgyia pseudotsugata) and one multicapsid (Orgyia pseudotsugata)]; one granulosis virus (Pieris brassicae); and NPVs from a hymenopteran (Neodiprion sertifer) and a dipteran (Tipula paludosa). Amino acid sequence data for the B. mori NPV were from a report by Serebryani et al. (1977) and that for the O. pseudotsugata NPVs were reported previously by us (Rohrmann et al. 1979). The other N-terminal amino acid sequences are presented in this paper. The phylogenetic relationships determined based on the molecular evolution of polyhedrin were also investigated by antigenic comparisons of the proteins using a solid phase radioimmune assay. The results indicate that the lepidopteran NPVs are the most closely related of the above group of viruses and are related to these viruses in the following order: N. sertifer NPV, P. brassicae granulosis virus, and T. paludosa NPV. These data, in conjunction with Baculovirus distribution and evidence concerning insect phylogeny, suggest that the Baculovirus have an ancient association with insects and may havae evolved along with them.

Applied and molecular aspects of insect granulosis viruses

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Biochemical and biophysical properties of a Mamestra brassicae multiple enveloped nuclear polyhedrosis virus

A multiply enveloped nuclear polyhedrosis virus from Mamestra brassicae has been shown to be morphologically similar to other baculoviruses. The virus particles contain 13 polypeptides of which 4 are associated with the nucleocapsid. The polyhedron comprises of one major polypeptide of molecular weight 28,000. The DNA has a mol. wt. of about 1.15 X 10(8), which is larger than that reported for other baculoviruses. The DNA is a circular, supercoiled molecule of CG mol. fraction 0.448. DNA fragments produced by a range of restriction enzymes are presented as an aid to identification.