PCR analysis of insertion site specificity, transcription, and structural uniformity of the Lepidopteran transposable element IFP2 in the TN-368 cell genome

The IFP2 element is a unique Lepidopteran transposon that has been associated with spontaneous Baculovirus mutants isolated following passage of the virus in the TN-368 cell line. Independent genomic representatives of IFP2 from TN-368 cells show little sequence divergence, suggesting that IFP2 was recently introduced into this genome and is highly stable. IFP2 is inserted within AT-rich regions of the TN-368 genome and targets TTAA sites. The specificity for TTAA target sites during transposition is not limited to the movement of IFP2 during an active Baculovirus infection, but is a property of its movement in uninfected cells as well. The exact origin of IFP2 remains obscure since it is found in two independently established Trichoplusia ni cell lines but not in three others, and we have not yet identified any IFP2 sequences in either field collected larvae or laboratory colonies.

Characterization of hitchhiker, a transposon insertion frequently associated with baculovirus FP mutants derived upon passage in the TN-368 cell line

We characterize a new Lepidopteran transposon associated with FP mutations of baculoviruses. This transposon, designated hitchhiker, is 579 bp long with 39-bp imperfect inverted terminal repeats. hitchhiker inserts with extreme specificity for a single trinucleotide target site, TTA, within the 25K gene. This transposon is the most frequently identified insertion in serial passage baculovirus mutants isolated from TN-368 cells.

A novel chemokine, macrophage inflammatory protein-related protein-2, inhibits colony formation of bone marrow myeloid progenitors

A new member of the beta-chemokine family, macrophage inflammatory protein (MIP)-related protein-2 (MRP-2) was isolated from a murine macrophage cell line, RAW 264.7. MRP-2 is composed of 122 amino acids of which the first 21 residues constitute a putative signal sequence. The putative mature protein is composed of 101 amino acids with a molecular weight of 11,600. MRP-2 is structurally similar to MIP-related protein-1 (MRP-1) (C10) and MIP-1 alpha. MRP-2 shows a 50.8% sequence identity at the protein level to MRP-1 and 46.3% identity to MIP-1 alpha. MRP-2 detects approximately 1.3 kilobase mRNA from monocyte and macrophage cell lines but does not detect the mRNA from T and B cells. The MRP-2 gene termed Scya9 was mapped to the central region of mouse chromosome 11 near the Scya1 and Scya2 genes, which are also members of the beta-chemokine superfamily. The Scya gene cluster was located between neurofibromatosis type 1 (Nf1) and myeloperoxidase (Mpo). rMRP-2 significantly suppressed colony formation by murine and human bone marrow granulocyte-macrophage (CFU-granulocyte-macrophage), erythroid (burst-forming unit-E), and multipotential (CFU-granulocyte-erythroid-macrophage-megakaryocyte) progenitor cells stimulated by combinations of growth factors.

A novel chemokine, macrophage inflammatory protein-related protein-2, inhibits colony formation of bone marrow myeloid progenitors

A new member of the beta-chemokine family, macrophage inflammatory protein (MIP)-related protein-2 (MRP-2) was isolated from a murine macrophage cell line, RAW 264.7. MRP-2 is composed of 122 amino acids of which the first 21 residues constitute a putative signal sequence. The putative mature protein is composed of 101 amino acids with a molecular weight of 11,600. MRP-2 is structurally similar to MIP-related protein-1 (MRP-1) (C10) and MIP-1 alpha. MRP-2 shows a 50.8% sequence identity at the protein level to MRP-1 and 46.3% identity to MIP-1 alpha. MRP-2 detects approximately 1.3 kilobase mRNA from monocyte and macrophage cell lines but does not detect the mRNA from T and B cells. The MRP-2 gene termed Scya9 was mapped to the central region of mouse chromosome 11 near the Scya1 and Scya2 genes, which are also members of the beta-chemokine superfamily. The Scya gene cluster was located between neurofibromatosis type 1 (Nf1) and myeloperoxidase (Mpo). rMRP-2 significantly suppressed colony formation by murine and human bone marrow granulocyte-macrophage (CFU-granulocyte-macrophage), erythroid (burst-forming unit-E), and multipotential (CFU-granulocyte-erythroid-macrophage-megakaryocyte) progenitor cells stimulated by combinations of growth factors.

Assay for movement of Lepidopteran transposon IFP2 in insect cells using a baculovirus genome as a target DNA

Mutagenesis of baculoviruses by host mobile elements occurs spontaneously and frequently during propagation of the viruses in Lepidopteran cell cultures. Most of the transposons identified as insertions in baculovirus genomes are relatively small Class II elements that exhibit a remarkable specificity for TTAA target sites. We have developed a transposition assay to analyze the movement of these TTAA-specific Lepidopteran transposons using the baculovirus genome as a target and a lacZ gene under control of the polyhedrin gene promoter as a selective marker for the transposon. This assay provides the first demonstration that a Lepidopteran transposon is capable of transposing while carrying a marker gene in insect cells. The data generated from this assay provide strong evidence that IFP2 encodes a protein that facilitates its own movement. This element may be used in a manner analogous to the P-element to mobilize genes in at least some Lepidopteran insect cells. Transposon tagging within the baculovirus genome identified several known genes and two previously undescribed open reading frames as nonessential to in vitro replication of the virus.

Endo-exonucleases: enzymes involved in DNA repair and cell death?

Endo-exonucleases from E. coli to man, although very different proteins, are multifunctional enzymes with similar enzymatic activities. They probably have two common but opposing biological roles. On the one hand, they promote survival of the organism by acting in recombination and recombinational DNA repair to diversify and help preserve the genome intact. On the other hand, they degrade the genomic DNA when it is damaged beyond repair. This ensures elimination of heavily mutagenized cells from the population.

TTAA serves as the target site for TFP3 lepidopteran transposon insertions in both nuclear polyhedrosis virus and Trichoplusia ni genomes

We have analysed TFP3 transposable elements from five independently isolated FP mutants of the Autographa californica nuclear polyhderosis virus (AcMNPV). We also analysed genomic copies of TFP3 elements amplified from the DNAs of the Trichoplusia ni cell line (TN-368) and T. ni larvae using the polymerase chain reaction (PCR). The sequences of all the newly isolated TFP3 elements closely resemble the previously described TFP3/1 element. Each of the transposons isolated from the virus mutants duplicated a TTAA tetranucleotide target site upon insertion into the viral genome. Four of these TFP3 elements transposed into three different 'TTAA' target sites within the 25 K gene (FP locus, map units 36-37 of AcMNPV). The fifth TFP3 element inserted at a 'TTAA' site within the AcMNPV Hin dIII-E fragment. One genomic TFP3 element, amplified from the TN-368 cell line DNA by an inverse PCR method, duplicated a 'TTAA' tetranucleotide target site that is present only once in the homologous larval DNA sequence. These data suggest that mobilization of TFP3 into both viral and cellular sites is identical in specificity and mechanism.

Cloning and sequence analysis of a p40 structural protein gene of Helicoverpa zea nuclear polyhedrosis virus

A gene encoding an occluded virion structural protein was isolated from an expression library constructed from the Helicoverpa zea S-type nuclear polyhedrosis virus (NPV) isolate HzS-15 using both polyclonal and monoclonal antibody screening. The gene was located within a Pstl-Sall fragment of the HzS-15 genome spanning from 96.5 to 97.3 m.u. Sequencing analyses revealed a long open reading frame of 927 nucleotides that predicted a protein of 37 kDa in size. Immunoblot analyses using the monoclonal antibody ENV409 demonstrated that the gene corresponded to a 40-kDa protein (p40) in SDS-polyacrylamide gels that was present exclusively in enveloped occluded virions but not in extracellular budded virions or envelope-stripped nucleocapsids. A p40 protein-specific transcript was detected at 16 hr postinfection in HzS-15-infected Hz 1075/UND-K cells and remained until 22 hr. Primer extension analyses demonstrated that the p40 protein-specific transcript started at -49 nucleotides from the ATG start codon within an ATAAG consensus pentamer found in late protein genes of Baculoviruses. The deduced amino acid sequence of the HzS-15 p40 protein gene shared 44 and 45% sequence homology with the p40 proteins of Bombyx mori NPV and Autographa californica NPV, respectively.

Expression of foreign epitopes on recombinant occlusion bodies of baculoviruses

Recombinant polyhedrin proteins of the baculovirus Autographa californica nuclear polyhedrosis virus were constructed to serve as immunologic carriers of foreign epitopes. Several recombinants containing an influenza haemagglutinin epitope were obtained. Three of the five recombinants formed occlusion bodies (OBs) and two did not. All of the recombinant polyhedrin proteins reacted with a monoclonal antibody (mAb) specific for an influenza epitope in Western blots. Presentation of the foreign epitope on the surface of recombinant OBs was demonstrated by specific immunoprecipitation of the anti-influenza mAb with recombinant OBs. The recombinant polyhedrin-influenza epitope fusion protein stimulated an influenza-specific immune response in rabbits.

A functional hepatitis B virus X protein produced in insect cells

We have constructed a recombinant baculovirus from Autographa californica nuclear polyhedrosis virus, called AcX, that expresses the gene encoding the hepatitis B virus X protein in infected Spodoptera frugiperda (Sf21AE) insect cells. A 16.5-kDa monomer and a 33-kDa dimer of the X protein were detected in extracts from AcX-infected cells on immunoblots using a polyclonal anti-X antibody. The biological activity of the insect cell-produced X protein was assayed by fusing AcX-infected Sf21AE cells with African green monkey kidney (CV-1) cells and then transfecting the fused cells with the reporter plasmid pSV2cat. The expression of the cat gene in CV-1:Sf21AE(AcX) fusions was seven times higher than that derived from CV-1:Sf21AE(AcMNPV) fusions, indicating that the insect cell-produced X protein was functional. The transactivation function of the insect cell-produced X protein was also verified by scrape-loading nuclear extracts of AcX-infected Sf21AE cells into pSV2cat-transfected CV-1 cells. Treatment of the AcX-infected cell nuclear extracts with anti-X antisera prior to scrape-loading eliminated the transactivating activity of the extracts. We conclude that the insect cell-produced X protein was functionally identical to that generated in mammalian cells.

Expression of two forms of carp gonadotropin alpha subunit in insect cells by recombinant baculovirus

There are two types of cDNA clones (designated alpha 1 and alpha 2) encoding the alpha subunit of carp gonadotropin. These two cDNAs are derived from different genes and encode proteins that differ by seven amino acid residues (three in the signal peptide and four in the mature polypeptide). Expression of these two cDNAs in insect cells by recombinant baculovirus revealed that the alpha 1 subunit, after noncovalent association with the beta subunit, has the same potency as the native alpha subunit purified from the pituitary. In contrast, the alpha 2 subunit can associate with the beta subunit, but only to form an inactive gonadotropin. Competition of the alpha 2 subunit with the alpha 1 subunit for association with the beta subunit decreases the gonadotropin activity of the alpha/beta complex. In addition, both alpha 1 and alpha 2 subunits are secreted into the culture medium by insect cells and have an apparent molecular mass approximately 5 kDa higher than that of the native alpha subunit. These results indicate that the insect cell-derived alpha 1 subunit is biologically active and that those four amino acid changes in the mature of alpha 2 protein affect the biological activity and thus provide valuable clues for the study of the structure-function relationship of the alpha subunit of glycoprotein hormones.

Direct double-stranded DNA sequencing with baculovirus genomes

Double-stranded DNA sequencing with the modified T7 DNA polymerase (Sequenase) was performed directly with nuclear polyhedrosis virus DNA genomes. The conditions were optimized to allow for a rapid and unambiguous sequence analysis of nuclear polyhedrosis virus genomes.

Oligosaccharide processing in the expression of human plasminogen cDNA by lepidopteran insect (Spodoptera frugiperda) cells

A comparison has been made between the Asn289-linked oligosaccharide structures of human plasma plasminogen and a recombinant human plasminogen, expressed in lepidopteran insect (Spodoptera frugiperda) cells, after infection of these cells with a recombinant baculovirus containing the entire human plasminogen cDNA. Using anion-exchange liquid chromatography mapping of the oligosaccharide units cleaved from the proteins by glycopeptidase F, compared with elution positions of standard oligosaccharide structures, coupled with monosaccharide compositional analysis, we find that the human plasma protein contained only bisialo-biantennary complex-type carbohydrate and asialo-biantennary complex carbohydrate, confirming earlier work published by this laboratory. The glycosylation pattern of the insect cell expressed recombinant human plasminogen showed considerable microheterogeneity, with identifiable high-mannose carbohydrate (Man9GlcNAc2) and truncated high-mannose oligosaccharide (Man5GlcNAc2, Man4GlcNAc2, and Man3GlcNAc2). Of major importance, approximately 40% of the oligosaccharide population consisted of complex carbohydrate (bisialo-biantennary), identical in structure with that of the human plasma protein. This is the first direct identification of complex carbohydrate in proteins produced in insect cells and demonstrates that trimming and processing of high-mannose carbohydrate into complex-type oligosaccharide can occur. Our data indicate that both normal and alternate pathways exist in these cells for incorporation and trimming of high-mannose oligosaccharides and that mannosidases, as well as galactosyl-, hexosaminidasyl-, and sialyltransferases are present, and/or can be induced, in these cells. From these observations, we conclude that amino acid sequences and/or protein conformational properties can control oligosaccharide processing events.

Endo-exonuclease of Aspergillus nidulans

Endo-exonuclease (EE) has been found in both active and inactive, but trypsin-activatable, forms in Aspergillus nidulans. Active EE was present mainly in nuclei, mitochondria, and vacuoles, while trypsin-activatable EE was mainly in the cytosol. The active form accounts for over 90% of the neutral deoxyribonuclease activity extracted from mycelia. A single strand (ss) DNA-binding EE associated with a 28 kilodalton (kDa) polypeptide was partially purified and characterized. It was found to closely resemble, in size and enzymological properties, the ss-DNA-binding EE previously purified from Neurospora crassa. Aspergillus nidulans EE was also found to be immunochemically related to the N. crassa EE and, like that enzyme, was probably derived from a polypeptide of 90 kDa or larger through proteolysis during extraction and purification. It had divalent metal ion-dependent (Mg2+, Mn2+, or Zn2+) activity on both DNA and RNA, which ultimately produced small 5'-P-terminated oligonucleotides. The nuclease activity was mixed endo- and exo-nucleolytic with ss-DNA as substrate, but largely exonucleolytic with double strand (ds) DNA. Superhelical phi X-174 DNA was nicked by EE to form relaxed circular and then linear ds-DNA, which was rapidly degraded to shorter fragments. Linearized pBR322 DNA was extensively nicked internally under conditions where there was relatively low exonuclease activity, but this nicking required that 5'-P-termini be present on the linear ds-DNA. The levels of active EE found in extracts of two recombination-deficient mutants of A. nidulans, uvsC and uvsE, dit not differ significantly from those in extracts of the wild type.

Neurospora endo-exonuclease is immunochemically related to the recC gene product of Escherichia coli

Immunochemical cross-reaction between the endo-exonuclease of Neurospora crassa, an enzyme previously implicated in recombination and recombinational DNA repair, and the recC-encoded polypeptide of Escherichia coli has been detected by immunoblotting extracts of strains of E. coli having a deletion that includes the recBCD genes but carrying multicopy plasmids bearing all three of the recBCD genes or only one or two of these genes. It was predicted that homology would also be found at the amino acid sequence level between the recC polypeptide and both nuclear and mitochondrial endo-exonucleases of Saccharomyces cerevisiae, which cross-react with antibodies raised to the N. crassa endo-exonuclease. Since the gene for the S. cerevisiae mitochondrial enzyme, NUC1, has been cloned and sequenced and the predicted amino acid sequence is known, this sequence was aligned with the predicted amino acid sequence of the recC polypeptide. Extensive homology was found by aligning 306 of the 329 amino acids of the yeast mitochondrial nuclease sequence with the carboxy-terminal one-quarter of the amino acid sequence of the recC polypeptide.

Transfection of cloned Heliothis zea cell lines with the DNA genome of the Heliothis zea nuclear polyhedrosis virus

Transfection conditions were optimized for the cloned UND-K derivative of the IPLB-HZ 1075 cell line using the calcium-phosphate co-precipitation technique and the DNA genome of the Heliothis zea S-type nuclear polyhedrosis virus. Optimal efficiencies were obtained using supercoiled viral DNA, and by extending the adsorption period for the diluted precipitate to 12 h. Transfection efficiencies ranging from 0.5 to 1.3 x 10(3) plaque forming units per microgram of supercoiled viral DNA were routinely obtained for UND-K cells and HzS-15 viral DNA. Transfection efficiencies were compared for 10 other cloned Heliothis cell strains and the uncloned parental IPLB-HZ 1075 cell line. The cloned cell strains UND-F, L, and U were incapable of transfection, while UND-I and G were 3 and 131 fold (respectively) less efficient than UND-K. The UND-K cells and the calcium phosphate transfection procedure permit relatively efficient in vitro manipulation of the Heliothis zea NPV virus genome.

Transposon mutagenesis of baculoviruses: analysis of TFP3 lepidopteran transposon insertions at the FP locus of nuclear polyhedrosis viruses

We report the complete sequences of two representatives of the TFP3 transposable element family of the lepidopteran, Trichoplusia ni. These elements were isolated as insertions mobilized from the Lepidopteran host genome into two closely related nuclear polyhedrosis viruses (NPV) during infection. Both elements inserted within the 500-bp FP locus of the respective viral genomes (map units 36.0 to 37.0), causing a distinctive plaque morphology phenotype and the loss of a 25-kDa viral-specific protein. Both insertions occurred at the identical TTAA target site in the respective genomes, in the same relative orientation, and are flanked by 15-bp imperfect inverted repeats. The inserted elements interrupt the 25K open reading frame (ORF). One of these FP mutants undergoes spontaneous reversion. Sequence analysis at the excision site of a spontaneous revertant demonstrates that the TFP3 elements are capable of precise excision, restoring the expression of the 25-kDa protein. We also compare the sequences of the 25K genes of the Autographa californica and Galleria mellonella viruses (AcMNPV and GmMNPV, respectively). The 25K gene sequences diverge in five areas, resulting in an additional EcoRV and TaqI site within the GmMNPV 25K gene, and extension of the ORF for an additional 2 amino acids at the C-terminus of the predicted GmMNPV 25 kDa protein. The phenomenon of transposon mutagenesis of Baculovirus genomes provides a unique opportunity for analysis of transposon mobility.

Transposon mutagenesis of baculoviruses: analysis of Trichoplusia ni transposon IFP2 insertions within the FP-locus of nuclear polyhedrosis viruses

The transposable IFP2 element of Trichoplusia ni was originally isolated as a host DNA insertion in spontaneous FP mutants of Galleria mellonella or Autographa californica nuclear polyhedrosis viruses (NPVs). The termini of IFP2 insertions from five independently isolated FP mutants were sequenced. In all cases IFP2 is flanked by 13-bp terminal inverted repeats and has additional inverted repeats of 19 bp in length located asymmetrically with respect to the ends of the element. Insertion of IFP2 into the viral genome always generated a duplication of the tetranucleotide target site, TTAA. There was an apparent preference for insertion within a 12-bp A + T-rich imperfect palindromic sequence surrounding the target site. Sequence analysis of three independent IFP2 elements revealed an internal domain of 2.475 kb containing an RNA polymerase II promoter region and two large open reading frames. Primer extension analysis of IFP2-specific mRNA positioned the 5' terminus of the transcript. The element is present in DNA isolated from T. ni cell lines TN-368 and TN-5B1, but is not apparent in DNAs isolated from the TN-R2 cell line or our laboratory colony of T. ni larvae, suggesting IFP2 was recently introduced into the T. ni genome.

The actions of Neurospora endo-exonuclease on double strand DNAs

Neurospora crassa endo-exonuclease, an enzyme implicated in recombinational DNA repair, was found previously to have a distributive endonuclease activity with a high specificity for single strand DNA and a highly processive exonuclease activity. The activities of endo-exonuclease on double strand DNA substrates have been further explored. Endo-exonuclease was shown to have a low bona fide endonuclease activity with completely relaxed covalently closed circular DNA and made site-specific breaks in linear double strand DNA at a low frequency while simultaneously generating a relatively high level of single strand breaks (nicks) in the DNA. Sequencing at nicks induced by endo-exonuclease in pBR322 restriction fragments showed that the highest frequency of nicking occurred at the mid-points of two sites with the common sequence, p-AGCACT-OH. In addition, sequencing revealed less frequent nicking at identical or homologous hexanucleotide sequences in all other 54 cases examined where these sequences either straddled the break site itself or were within a few nucleotides on either side of the break site. The exonucleolytic action of endo-exonuclease on linear DNA showed about 100-fold preference for acting in the 5' to 3' direction. Removal of the 5'-terminal phosphates substantially reduced this activity, internal nicking, and the ability of endo-exonuclease to generate site-specific double strand breaks. On the other hand, nicking of the dephosphorylated double strand DNA with pancreatic DNase I stimulated the exonuclease activity by almost 5-fold, but no stimulation was observed when the DNA was nicked by Micrococcal nuclease. Thus, 5'-p termini either at double strand ends or at nicks in double strand DNA are entry points to the duplex from which endo-exonuclease diffuses linearly or "tracks" in the 5' to 3' direction to initiate its major endo- and exonucleolytic actions. The results are interpreted to show how it is possible for endo-exonuclease to generate single strand DNA for switching into a homologous duplex either at a nick or while remaining bound at a double strand break in the DNA. Such mechanisms are consistent with current models for recombinational double strand break repair in eukaryotes.

Expression of human plasminogen cDNA in a baculovirus vector-infected insect cell system

A cDNA that encodes the human plasminogen (HPg) amino acid sequence has been inserted adjacent to the polyhedrin promoter in the genome of the baculovirus, Autographa californica nuclear polyhedrosis virus, which was then used to infect cultured cells of the farm armyworm, Spodoptera frugiperda. Under the conditions of cell growth employed, recombinant (rec)-HPg was secreted into the medium after 24 h postinfection (p.i.), at which point virtually no rec-HPg antigen remained inside the cells. At 48 h p.i., a maximal level of intact rec-HPg was present in the medium, which underwent substantial proteolytic digestion after that time. The rec-HPg produced by this expression system possessed a molecular weight equivalent to that of plasma [Glu1]-plasminogen. In addition, the rec-HPg adsorbed to Sepharose-lysine, and was eluted with epsilon-aminocaproic acid (EACA). The recombinant protein also interacted with polyclonal antibodies generated to plasma HPg, as well as with a monoclonal antibody directed against a distinct region (kringle 1-3) of the plasma HPg molecule. Finally, the insect-expressed rec-HPg was activatable to plasmin (HPm) by urokinase. The results demonstrate that this expression system produces a full-length functional single-chain rec-HPg, which can be isolated intact from the culture medium, with some consideration for the temporal events that occur in secretion and longer-term degradation of the protein. The fact that this rec-HPg was converted to HPm with a plasminogen activator, and that it interacted with anti-plasma HPg polyclonal and monoclonal antibodies, as well as with the ligand, EACA, indicates that the molecule retains many of its important functional properties and is folded in an integral manner.

A single, phosphate-repressible deoxyribonuclease, DNase A, secreted in Aspergillus nidulans

High levels of nuclease activities were identified in filtrates of Aspergillus cultures after growth in low-but not in high-phosphate media. Deoxyribonuclease activities, characterized extensively by column chromatography, showed a coincident single peak for ss- and ds-DNase which was distinct from the peak for RNase. Both ss-DNase and ds-DNase are endonucleolytic and showed the highest activity in the presence of Ca2+ and Mn2+ (at pH 8.0). They also showed identical heat sensitivities suggesting that a single, phosphate-repressible DNase was secreted. This enzyme, therefore, corresponds to the well-characterized extracellular DNase A of Neurospora. However, the Aspergillus DNase A did not cross-react with antisera to secreted Neurospora nucleases and showed different chromatographic properties, and active peptides of different sizes were visualized on DNA activity gels. The increasing derepression of Aspergillus DNase A by decreasing phosphate levels was similar to that of secreted alkaline phosphatase and these increases were both abolished by the regulatory mutant palcA.