Characterization of the Spodoptera frugiperda TATA-binding protein: nucleotide sequence and response to baculovirus infection

Characterization of cDNAs encoding p53 of Bombyx mori and Spodoptera frugiperda

Complementary DNAs encoding homologs of the tumor suppressor gene, p53, were characterized from two lepidopteran insects, Bombyx mori (Bm) and Spodoptera frugiperda (Sf). They encoded predicted proteins of 368 (41.2 kDa) (Bm) and 374 (42.5 kDa) (Sf) amino acids. The sequences shared 44% amino acid and 60% nucleotide sequence identity with each other, but exhibited less than 20% amino acid and 46% nucleotide sequence identity to Drosophila melanogaster p53. Despite the sequence diversity, conserved amino acids involved in DNA and zinc binding were present in the lepidopteran sequences. Expression of Sfp53-induced apoptosis in S. frugiperda cells, and antiserum made against recombinant Sfp53 recognized a protein whose abundance increased after treatment with DNA damaging agents.

Penaeus monodon TATA box-binding protein interacts with the white spot syndrome virus transactivator IE1 and promotes its transcriptional activity

We show here that the white spot syndrome virus (WSSV) immediate-early protein IE1 interacts with the Penaeus monodon TATA box-binding protein (PmTBP) and that this protein-protein interaction occurs in the absence of any other viral or cellular proteins or nucleic acids, both in vitro and in vivo. Mapping studies using enhanced green fluorescent protein (EGFP) fusion proteins containing truncations of IE1 and PmTBP delimited the interacting regions to amino acids (aa) 81 to 180 in IE1 and, except for aa 171 to 230, to aa 111 to 300 in PmTBP. A WSSV IE1 transactivation assay showed that large quantities (>800 ng) of the GAL4-IE1 plasmid caused "squelching" of the GAL4-IE1 activity and that this squelching effect was alleviated by the overexpression of PmTBP. Gene silencing of WSSV ie1 and PmTBP by pretreatment with double-stranded RNAs (dsRNAs) prior to WSSV challenge showed that the expression of these two target genes was specifically inhibited by their corresponding dsRNAs 72 and 96 h after dsRNA treatment. dsRNA silencing of ie1 and PmTBP expression also significantly reduced WSSV replication and the expression of the viral early gene dnapol (DNA polymerase gene). These results suggest that WSSV IE1 and PmTBP work cooperatively with each other during transcription initiation and, furthermore, that PmTBP is an important target for WSSV IE1's transactivation activity that can enhance viral gene expression and help in virus replication.

A genomic BAC library and a new BAC-GFP vector to study the holocentric pest Spodoptera frugiperda

Two genomic tools for the study of Lepidoptera and the holocentric structure of their chromosomes are presented in this paper. A bacterial artificial chromosome (BAC) library was constructed using nuclear DNA partially digested with HindIII from eggs of Spodoptera frugiperda. The library contains a total of 36,864 clones with an average insert size of 125 kb, which corresponds to approximately 11.5 genome equivalents. Hybridization screening of the library was performed with eight single-copy genes, giving an average hit of 10 clones per marker gene. Colinearity between the genome and BACs was demonstrated at the triose phosphate isomerase (tpi) locus. Probing of the library with a PCR fragment internal to the 18S ribosomal gene allowed an estimation of the rDNA locus size close to 115 repeats per haploid genome. A new vector (pBAC3.6eGFP) for transient transfection into S. frugiperda cell lines has been constructed. It is based on the BAC vector, pBAC3.6e, in which a gene encoding GFP was inserted under the control of the densovirus P9 promoter. This vector has the advantage to accommodate large genomic inserts and to be transfected in a large lepidopteran host range. It was used to construct a second BAC library from Sf9 cell nuclear DNA in order to allow a comparison between somatic and cell line genome organization.

Baculovirus infection raises the level of TATA-binding protein that colocalizes with viral DNA replication sites

During the infection cycle of Autographa californica multicapsid nuclear polyhedrosis virus, the TATA-binding protein (TBP) of the insect host cell likely participates in early viral transcription, which is mediated by the host RNA polymerase II. However, the role of TBP in late and very late viral transcription, which is accomplished by an alpha-amanitin-resistant RNA polymerase, is unclear. We observed a dramatic increase of TBP protein during the late phases of infection. TBP mRNA levels, however, were not coordinately increased. Indirect-immunofluorescence studies revealed a nuclear redistribution of TBP during infection. After labeling of viral replication centers with bromodeoxyuridine (BrdU), costaining of TBP and BrdU showed that TBP localized to viral DNA replication centers. These results suggest a putative role of TBP during late viral transcription, which may occur in close proximity to viral DNA replication.

Characterization of a baculovirus alkaline nuclease

All baculovirus genomes sequenced to date encode a homolog of an alkaline nuclease that has been characterized in the Herpesviridae. In this report we describe the characterization of the alkaline nuclease (AN) homolog of the Autographa californica multinucleocapsid nucleopolyhedrovirus (AcMNPV) (open reading frame 133). His-tagged AN constructs were expressed in recombinant baculoviruses and affinity purified, and then their enzymatic activity was characterized. AN was found to degrade linear DNA at alkaline pH, preferred Mg(2+) over Mn(2+), had optimal activity at 35 degrees C, and did not appear to have a salt requirement. To rule out contamination by the endogenous baculovirus gene product or a cellular enzyme, point mutations were introduced into a highly conserved domain of the gene. These mutations were found to markedly reduce or eliminate most of the activity of the affinity-purified enzyme. An antibody generated against the protein was used to analyze its expression by Western blot analysis. AN was found to be expressed at low levels by 12 h postinfection, with maximal expression at 24 h postinfection. Attempts to generate a virus with this gene inactivated were unsuccessful, suggesting that AN may be encoded by an essential gene.

The TATA binding protein in the sea urchin embryo is maternally derived

The cDNA encoding the TATA binding protein was isolated from 8- to 16-cell and morula-stage embryonic libraries of two distantly related species of sea urchin, Strongylocentrotus purpuratus and Lytechinus variegatus, respectively. The two proteins are 96% identical over both the N- and C-terminal domains, suggesting a conservation of transcriptional processes between the two species. The prevalence of SpTBP transcripts at several developmental time points was determined using the tracer excess titration method, and the corresponding number of TBP protein molecules was determined by quantitative Western blot analysis. Our results indicate that the amount of TBP mRNA and protein per embryo remains relatively constant throughout development. An initial large pool of TBP protein (>10(9)) molecules in the egg becomes diluted as a consequence of cell division and decreases to about 2 x 10(6) molecules per cell by the gastrula stage. We found by in situ RNA hybridization that the oocyte contains a large amount of TBP mRNA which is depleted late in oogenesis so that the eggs and early embryos have extremely low levels of TBP mRNA. We conclude that the oocyte manufactures nearly all of the TBP protein necessary for embryogenesis.

The host factor polyhedrin promoter binding protein (PPBP) is involved in transcription from the baculovirus polyhedrin gene promoter

Hypertranscription and temporal expression from the Autographa californica nuclear polyhedrosis (AcNPV) baculovirus polyhedrin promoter involves an alpha-amanitin-resistant RNA polymerase and requires a trans-acting viral factor(s). We previously reported that a 30-kDa host factor, polyhedrin promoter binding protein (PPBP), binds with unusual affinity, specificity, and stability to the transcriptionally important motif AATAAATAAGTATT within the polyhedrin (polh) initiator promoter and also displays coding strand-specific single-stranded DNA (ssDNA)-binding activity (S. Burma, B. Mukherjee, A. Jain, S. Habib, and S. E. Hasnain, J. Biol. Chem. 269:2750-2757, 1994; B. Mukherjee, S. Burma, and S. E. Hasnain, J. Biol. Chem. 270:4405-4411, 1995). We now present evidence which indicates that an additional factor(s) is involved in stabilizing PPBP-duplex promoter and PPBP-ssDNA interactions. TBP (TATA box binding protein) present in Spodoptera frugiperda (Sf9) cells is characteristically distinct from PPBP and does not interact directly with the polh promoter. Replacement of PPBP cognate sequences within the polh promoter with random nucleotides abolished PPBP binding in vitro and also failed to express the luciferase reporter gene in vivo. Phosphocellulose fractions of total nuclear extract from virus-infected cells which support in vitro transcription from the polh promoter contain PPBP activity. When PPBP was sequestered by the presence of oligonucleotides containing PPBP cognate sequence motifs, in vitro transcription of a C-free reporter cassette was affected but was restored by the exogenous addition of nuclear extract containing PPBP. When PPBP was mopped out in vivo by a plasmid carrying PPBP cognate sequence present in trans, polh promoter-driven expression of the luciferase reporter was abolished, demonstrating that binding of PPBP to the polh promoter is essential for transcription.

Characterization of P91, a protein associated with virions of an Orgyia pseudotsugata baculovirus

Polyclonal antiserum produced against preoccluded virions from the Orgyia pseudotsugata multinucleocapsid nuclear polyhedrosis virus (OpMNPV) was used to screen an OpMNPV lambda gt11 expression library. The insert from one of the immunoreactive phage isolates hybridized to OpMNPV orf86 (p91), a 2460-bp (819 amino acids) open reading frame that encodes a predicted protein of 91 kDa. Antibodies generated against a maltose binding protein-P91 fusion detected a band of approximately 91 kDa on Western blots of extracts of OpMNPV-infected Lymantria dispar cells. This band was first observed at 18 hr p.i. and was present at all later time points. Similar results using this antiserum were seen with a time course of Autographa californica-infected Spodoptera frugiperda cells. Localization of P91 by confocal immunofluorescence microscopy showed that the protein was concentrated near the nuclear membrane and at late times p.i. was most concentrated near polyhedra. Immunoelectron microscopy indicated that P91 was present in both the capsid and envelope surrounding the capsid of occlusion-derived virions. Fractionation studies employing NP-40 and Western blot analysis indicated that P91 was associated with the capsid structure.

A 30-kDa host protein binds to two very-late baculovirus promoters

A 30-kDa host factor (polyhedrin-promoter-binding protein; PPBP) specifically binds to sequences critical for transcription from the baculovirus polyhedrin (p29) gene initiator promoter [Burma, S., Mukherjee, B., Jain, A., Habib, S. & Hasnain, S. E. (1994) J. Biol. Chem. 269, 2750-2757; Mukherjee, B., Burma, S. & Hasnain, S. E. (1995) J. Biol. Chem. 270, 4405-4411]. A host factor also binds, in gel shift assays, to the very-late p10 gene promoter through DNA sequence motifs similar to the PPBP.p29 interaction. The p10 host factor complex was specifically competed out with oligonucleotides containing p29 cognate sequence motifs AATAAA and TAAGTATT, but this did not occur when these motifs were replaced with random sequences. From ultraviolet cross-linking analysis, the molecular mass of this host factor was estimated to be approximately 30 kDa. Experiments were performed to investigate if this host factor displayed any differences in affinity and turnover with respect to the p29 and p10 untranslated leader sequences known to be important for temporal fine tuning and the late burst of transcription. Half-life determination of the p10-binding protein revealed similar binding affinities for the initiator elements of both the promoters, but higher affinity for the p10 5'-untranslated region (approximately 30 min versus approximately 10 min). The involvement of a similar host factor binding to both the p10 and p29 promoters indicates the possibility of a similar mode of transcription initiation from these two very-late promoters.

Expression of PE38 and IE2, viral members of the C3HC4 finger family, during baculovirus infection: PE38 and IE2 localize to distinct nuclear regions

The pe38 gene of Autographa californica nuclear polyhedrosis virus represents one of the major early transcripts after viral infection. The function of the pe38 protein, which contains a C3HC4 zinc finger motif, is still not understood. We have raised polyclonal antiserum against the pe38 protein, PE38, produced in bacteria to investigate pe38 expression in the course of infection. A approximately 38-kDa polypeptide is first detectable at 2 h postinfection and decreases rapidly after 24 h. During the late phases of infection, a smaller protein of approximately 20 kDa which cross-reacts with the PE38-specific antiserum is visible at a constant level until 120 h postinfection. Since the pe38 gene shares a divergent promoter unit with the ie2 gene (formerly IEN), we have compared the expressions of the two genes. Polyclonal antibodies were raised against the bacterially expressed ie2 protein. The temporal expression pattern of the approximately 49-kDa ie2 protein is comparable to that of the approximately 38-kDa pe38 protein. Furthermore, both proteins are present in the nuclear fraction of A. californica nuclear polyhedrosis virus-infected Spodoptera frugiperda cells, but the approximately 38-kDa pe38 protein is also detectable in the cytoplasm while the smaller protein of approximately 20 kDa is exclusively present in the cytoplasmic fraction. Immunofluorescence analysis reveals that PE38 and IE2 localize to distinct regions within the nucleus mainly detected after transfection of pe38- and ie2-expressing constructs.