Gene Expression Vector Research Articles

Prokaryotic Expression of AATF-Che1 Superfamily Gene and Its Fusion Protein Purification

Objective To construct the apoptosis antagonizing transcription factor (AATF)-Che1 recombinant prokaryotic expression vector pGEX-4T-1-AATF-Che1 in vitro,optimize prokaryotic recombinant vector induced expression conditions,and get soluble purified glutathione S-transferase(GST) fusion proteins.Methods The AATF-Che1 gene was amplificated from the pGEX-4T-1-AATF recombinant plasmid by polymerase chain reaction(PCR).The prokaryotic expression vector pGEX-4T-1 was digested with double enzymes,and recycled purpose fragments.The directional connection of AATF-Che1 gene and linearization prokaryotic expression vector pGEX-4T-1 were through the T4 ligase,to obtain recombinant protein AATF-Che1 prokaryotic expression plasmid pGEX-4T-1-AATF-Che1.Correct plasmid was transformated to escherichia coli cells BL21 (DE3),and used isopropy1β-D-1-thiogalactopyranoside (IPTG) to induce AATF-Che1 protein expression.Through exploring the influence of the IPTG concentration,induction time and temperature to the expression quantity and form of the recombinant protein,optimized the best induction conditions.Using glutathione sepharose beads purificated soluble GST fusion protein,at last to identificate of the protein by Western blot (WB) mothd.Results The results of enzyme digestion,PCR identification and sequencing were correct,and the prokaryotic expression plasmid was successfully constructed.The electrophoresis showed that a new protein band appear at about 65 kD,which was the fusion protein of AATF-Che1 and GST.The fusion protein was no obvious change with different induction time and IPTG concentration at 37℃ or 16℃.The recombinant protein mainly existed in the form of inclusion body at 37 ℃,while soluble from in the supernatant at 16℃.Soluble purificated GST fusion protein was obtained,and by WB method identified antigenicity of fusion protein was good.Conclusions The prokaryotic expression plasmid was successfully constructed in vitro.The optimized recombinant prokaryotic expression conditions were found and purificated GST fusion protein was obtained.It maybe lay the foundation for the further study on the role of AATF-Che1 in tumor. Key words: AATF-Che1 superfamily domain; Prokaryotic expression; Fusion protein purification

Gamma-retroviral vector design for the co-expression of artificial microRNAs and therapeutic proteins.

To generate γ-retroviral vectors for stable conjoint expression of artificial microRNAs (amiR) and therapeutic genes in primary human lymphocytes, and to identify the design parameters that are key for successful vector generation. Gamma-retroviral vectors were designed to co-express both amiRs and a linked reporter gene, truncated CD34 (tCD34). Artificial miRs based on microRNAs miR-16, miR-142, miR-146b, miR-150, miR155, and miR-223 were inserted into sites within the intron of the vector and tested for tCD34 expression by flow cytometry (FACS). Different constructs were assembled with amiRs targeted to knockdown expression of suppressor of cytokine signaling 1 (SOCS1) or programmed cell death 1 (PDCD1, PD-1). Three of the six amiRs maintained tCD34 expression. Expansion of primary human T cells transduced with these amiR vectors, as well as transgene expression, were equivalent to control engineered T cells over a 40-day period. Knockdown of SOCS1 RNA and PD-1 expression by FACS was shown to vary between constructs, dependent on either the specific short interfering RNA sequence used in the amiR, or the microRNA backbone and location in the vector intron. Gamma-retroviral vectors that both efficiently knockdown endogenous gene expression and maintain linked transgene production can be produced, but empirical vector evaluations were best suited for optimal construct analysis.

Versatile and stable vectors for efficient gene expression in Ralstonia eutropha H16

The Gram-negative β-proteobacterium Ralstonia eutropha H16 is primarily known for polyhydroxybutyrate (PHB) production and its ability to grow chemolithoautotrophically by using CO2 and H2 as sole carbon and energy sources. The majority of metabolic engineering and heterologous expression studies conducted so far rely on a small number of suitable expression systems. Particularly the plasmid based expression systems already developed for the use in R. eutropha H16 suffer from high segregational instability and plasmid loss after a short time of fermentation. In order to develop efficient and highly stable plasmid expression vectors for the use in R. eutropha H16, a new plasmid design was created including the RP4 partitioning system, as well as various promoters and origins of replication. The application of minireplicons derived from broad-host-range plasmids RSF1010, pBBR1, RP4 and pSa for the construction of expression vectors and the use of numerous, versatile promoters extend the range of feasible expression levels considerably. In particular, the use of promoters derived from the bacteriophage T5 was described for the first time in this work, characterizing the j5 promoter as the strongest promoter yet to be applied in R. eutropha H16. Moreover, the implementation of the RP4 partition sequence in plasmid design increased plasmid stability significantly and enables fermentations with marginal plasmid loss of recombinant R. eutropha H16 for at least 96h. The utility of the new vector family in R. eutropha H16 is demonstrated by providing expression data with different model proteins and consequently further raises the value of this organism as cell factory for biotechnological applications including protein and metabolite production.

Versatile and stable vectors for efficient gene expression in Ralstonia eutropha H16

The Gram-negative β-proteobacterium Ralstonia eutropha H16 is primarily known for polyhydroxybutyrate (PHB) production and its ability to grow chemolithoautotrophically by using CO2 and H2 as sole carbon and energy sources. The majority of metabolic engineering and heterologous expression studies conducted so far rely on a small number of suitable expression systems. Particularly the plasmid based expression systems already developed for the use in R. eutropha H16 suffer from high segregational instability and plasmid loss after a short time of fermentation. In order to develop efficient and highly stable plasmid expression vectors for the use in R. eutropha H16, a new plasmid design was created including the RP4 partitioning system, as well as various promoters and origins of replication. The application of minireplicons derived from broad-host-range plasmids RSF1010, pBBR1, RP4 and pSa for the construction of expression vectors and the use of numerous, versatile promoters extend the range of feasible expression levels considerably. In particular, the use of promoters derived from the bacteriophage T5 was described for the first time in this work, characterizing the j5 promoter as the strongest promoter yet to be applied in R. eutropha H16. Moreover, the implementation of the RP4 partition sequence in plasmid design increased plasmid stability significantly and enables fermentations with marginal plasmid loss of recombinant R. eutropha H16 for at least 96 h. The utility of the new vector family in R. eutropha H16 is demonstrated by providing expression data with different model proteins and consequently further raises the value of this organism as cell factory for biotechnological applications including protein and metabolite production.

PSiM24 Is a Novel Versatile Gene Expression Vector for Transient Assays As Well As Stable Expression of Foreign Genes in Plants

We have constructed a small and highly efficient binary Ti vector pSiM24 for plant transformation with maximum efficacy. In the pSiM24 vector, the size of the backbone of the early binary vector pKYLXM24 (GenBank Accession No. HM036220; a derivative of pKYLX71) was reduced from 12.8 kb to 7.1 kb. The binary vector pSiM24 is composed of the following genetic elements: left and right T-DNA borders, a modified full-length transcript promoter (M24) of Mirabilis mosaic virus with duplicated enhancer domains, three multiple cloning sites, a 3′rbcsE9 terminator, replication functions for Escherichia coli (ColE1) and Agrobacterium tumefaciens (pRK2-OriV) and the replicase trfA gene, selectable marker genes for kanamycin resistance (nptII) and ampicillin resistance (bla). The pSiM24 plasmid offers a wide selection of cloning sites, high copy numbers in E. coli and a high cloning capacity for easily manipulating different genetic elements. It has been fully tested in transferring transgenes such as green fluorescent protein (GFP) and β-glucuronidase (GUS) both transiently (agro-infiltration, protoplast electroporation and biolistic) and stably in plant systems (Arabidopsis and tobacco) using both agrobacterium-mediated transformation and biolistic procedures. Not only reporter genes, several other introduced genes were also effectively expressed using pSiM24 expression vector. Hence, the pSiM24 vector would be useful for various plant biotechnological applications. In addition, the pSiM24 plasmid can act as a platform for other applications, such as gene expression studies and different promoter expressional analyses.

A versatile system for USER cloning-based assembly of expression vectors for mammalian cell engineering.

A new versatile mammalian vector system for protein production, cell biology analyses, and cell factory engineering was developed. The vector system applies the ligation-free uracil-excision based technique – USER cloning – to rapidly construct mammalian expression vectors of multiple DNA fragments and with maximum flexibility, both for choice of vector backbone and cargo. The vector system includes a set of basic vectors and a toolbox containing a multitude of DNA building blocks including promoters, terminators, selectable marker- and reporter genes, and sequences encoding an internal ribosome entry site, cellular localization signals and epitope- and purification tags. Building blocks in the toolbox can be easily combined as they contain defined and tested Flexible Assembly Sequence Tags, FASTs. USER cloning with FASTs allows rapid swaps of gene, promoter or selection marker in existing plasmids and simple construction of vectors encoding proteins, which are fused to fluorescence-, purification-, localization-, or epitope tags. The mammalian expression vector assembly platform currently allows for the assembly of up to seven fragments in a single cloning step with correct directionality and with a cloning efficiency above 90%. The functionality of basic vectors for FAST assembly was tested and validated by transient expression of fluorescent model proteins in CHO, U-2-OS and HEK293 cell lines. In this test, we included many of the most common vector elements for heterologous gene expression in mammalian cells, in addition the system is fully extendable by other users. The vector system is designed to facilitate high-throughput genome-scale studies of mammalian cells, such as the newly sequenced CHO cell lines, through the ability to rapidly generate high-fidelity assembly of customizable gene expression vectors.

307. Engineering Recombinant AAV Vectors for More Efficient and Restricted Gene Expression in the CNS after Systemic Administration

We previously demonstrated that delivery of the cytokine leukemia inhibitory factor (LIF) to the brain by recombinant adenovirus enhances oligodendrocyte progenitor cell proliferation and remyelination in a mouse model of multiple sclerosis (MS).

IRES-incorporated lactococcal bicistronic vector for target gene expression in a eukaryotic system

Plasmid DNAs isolated from lactic acid bacteria (LAB) such as Lactococcus lactis (L. lactis) has been gaining more interests for its positive prospects in genetic engineering-related applications. In this study, the lactococcal plasmid, pNZ8048 was modified so as to be able to express multiple genes in the eukaryotic system. Therefore, a cassette containing an internal ribosome entry site (IRES) was cloned between VP2 gene of a very virulent infectious bursal disease (vvIBDV) UPM 04190 of Malaysian local isolates and the reporter gene, green fluorescent protein (GFP) into pNZ:CA, a newly constructed derivative of pNZ8048 harboring the cytomegalovirus promoter (Pcmv) and polyadenylation signal. The new bicistronic vector, denoted as pNZ:vig was subjected to in vitro transcription/translation system followed by SDS–PAGE and Western blot analysis to rapidly verify its functionality. Immunoblotting profiles showed the presence of 49 and 29kDa bands that corresponds to the sizes of the VP2 and GFP proteins respectively. This preliminary result shows that the newly constructed lactococcal bicistronic vector can co-express multiple genes in a eukaryotic system via the IRES element thus suggesting its feasibility to be used for transfection of in vitro cell cultures and vaccine delivery.

Disrupting the methionine biosynthetic pathway in Candida guilliermondii: characterization of the MET2 gene as counter‐selectable marker

Candida guilliermondii (teleomorph Meyerozyma guilliermondii) is an ascomycetous species belonging to the fungal CTG clade. This yeast remains actively studied as a result of its moderate clinical importance and most of all for its potential uses in biotechnology. The aim of the present study was to establish a convenient transformation system for C. guilliermondii by developing both a methionine auxotroph recipient strain and a functional MET gene as selection marker. We first disrupted the MET2 and MET15 genes encoding homoserine-O-acetyltransferase and O-acetylserine O-acetylhomoserine sulphydrylase, respectively. The met2 mutant was shown to be a methionine auxotroph in contrast to met15 which was not. Interestingly, met2 and met15 mutants formed brown colonies when cultured on lead-containing medium, contrary to the wild-type strain, which develop as white colonies on this medium. The MET2 wild-type allele was successfully used to transfer a yellow fluorescent protein (YFP) gene-expressing vector into the met2 recipient strain. In addition, we showed that the loss of the MET2-containing YFP-expressing plasmid can be easily observed on lead-containing medium. The MET2 wild-type allele, flanked by two short repeated sequences, was then used to disrupt the LYS2 gene (encoding the α-aminoadipate reductase) in the C. guilliermondii met2 recipient strain. The resulting lys2 mutants displayed, as expected, auxotrophy for lysine. Unfortunately, all our attempts to pop-out the MET2 marker (following the recombination of the bordering repeat sequences) from a target lys2 locus were unsuccessful using white/brown colony colour screening. Nevertheless, this MET2 transformation/disruption system represents a new versatile genetic tool for C. guilliermondii.

A new series of vectors for constitutive, inducible or repressible gene expression in Candida guilliermondii

The biotechnological potential of C. guilliermondii is now well established. This yeast species currently benefits from the availability of a convenient molecular toolbox including recipient strains, selectable markers and optimized transformation protocols. However, the number of expression systems for biotechnological applications in C. guilliermondii remains limited. We have therefore developed and characterized a new series of versatile controllable expression vectors for this yeast. While previous studies firmly demonstrated that knock-out systems represent efficient genetic strategies to interrupt yeast biochemical pathways at a specific step in C. guilliermondii, the set of expression plasmids described in this study will provide new powerful opportunities to boost homologous or heterologous biosynthetic routes by fine controlled over-expression approaches.

Synthetic biology platform of CoryneBrick vectors for gene expression in Corynebacterium glutamicum and its application to xylose utilization

Currently, the majority of tools in synthetic biology have been designed and constructed for model organisms such as Escherichia coli and Saccharomyces cerevisiae. In order to broaden the spectrum of organisms accessible to such tools, we established a synthetic biological platform, called CoryneBrick, for gene expression in Corynebacterium glutamicum as a set of E. coli-C. glutamicum shuttle vectors whose elements are interchangeable with BglBrick standard parts. C. glutamicum is an established industrial microorganism for the production of amino acids, proteins, and commercially promising chemicals. Using the CoryneBrick vectors, we showed various time-dependent expression profiles of a red fluorescent protein. This CoryneBrick platform was also applicable for two-plasmid expression systems with a conventional C. glutamicum expression vector. In order to demonstrate the practical application of the CoryneBrick vectors, we successfully reconstructed the xylose utilization pathway in the xylose-negative C. glutamicum wild type by fast BglBrick cloning methods using multiple genes encoding for xylose isomerase and xylulose kinase, resulting in a growth rate of 0.11 ± 0.004h(-1) and a xylose uptake rate of 3.35mmol/gDW/h when 1% xylose was used as sole carbon source. Thus, CoryneBrick vectors were shown to be useful engineering tools in order to exploit Corynebacterium as a synthetic platform for the production of chemicals by controllable expression of the genes of interest.

Construction of a shuttle vector for inducible gene expression in Borrelia burgdorferi

Objective To construct a shuttle plasmid for inducible gene expression in Borrelia burgdorferi (B.burgdorferi) with an advantage of flexible genetic manipulation.Methods The IPTG-inducible lac repressor/operator system from Escherichia coli (E.coli) was adopted and modified in the current study.The plasmid shuttle vector was developed by inserting multiple cloning sites,FLAG and HA tags into the shuttle vector by molecular cloning approaches.The target gene was inserted at the site under the control of the promoter (Tn5 derivate) in plasmid pQE30.This promoter contained two lac operators and a codonoptimized lacI gene driven by flaB promoter.Results A plasmid shuttle vector,pJJ275,was successfully constructed with the ability to express target genes in B.burgdorferi in the presence of IPTG.By using this system,a HA-tagged rpoS gene was introduced into the typical infectious strain B.burgdorferi B31.The target gene expression induced by IPTG was confirmed at transcriptional and translational levels.The RpoS dependent virulence factor of Borrelia,OspC,was also detected,indicating that the expressed protein was functional.Conclusion The constructed plasmid shuttle vector can express exogenous genes in B.burgdorferi with an inducible feature and an advantage of flexible genetic manipulation.It can be applied for genetic manipulation of B.burgdorferi involved in gene regulation and complementation. Key words: Borrelia burgdorferi; Shuttle vector; Induced expression; Tool plasmid

High Efficiency Transfection of Embryonic Limb Mesenchyme With Plasmid DNA Using Square Wave Pulse Electroporation and Sucrose Buffer

Micromass cultures of primary embryonic limb mesenchyme are a valuable model system for studying cartilage formation in vitro. However, high efficiency introduction of plasmid DNA into this hard-to-transfect cell type typically results in considerable cell death and significantly impeded chondrogenesis when the cells are subsequently plated in high density micromass. Here, we describe a novel method in which square wave pulse electroporation of chick embryo wing bud mesenchyme suspended in protective sucrose buffer results in high efficiency transfection without substantially affecting micromass culture cell viability or chondrogenic differentiation potential. Furthermore, we show that this protocol can be employed, along with effector gene expression vectors, to generate observable changes in the amount of cartilage tissue formed in micromass, unlike lower efficiency, higher cytotoxicity techniques that require co-transfection of reporter plasmids to monitor changes in the extent of chondrogenesis and correct for differences in cell viability.

Histidinylated poly-L-lysine-based vectors for cancer-specific gene expression via enhancing the endosomal escape

In this work, we synthesized a series of poly-L-lysine (PLL)-based polymers for gene delivery, by modifying the PLL with both cationic peptide and histidine. The peptide moieties serve as cationic centers for polyplex formation, and also as substrates for protein kinase Cα (PKCα), which is specifically activated in many types of cancer cells, to achieve cancer-specific gene expression. The histidine groups serve as buffering moieties to increase the ability of the plasmid DNA (pDNA)-polymer complex (polyplex) to escape the endosome and thus to promote expression of the pDNA in the transfected cells. The facile synthesis of the polymers proceeded by modifying the PLL with side-group-protected peptide and protected histidine, followed by deprotection of the functional groups. The synthesized polymers showed significant buffering capacity over the neutral to acidic pH range and showed less cytotoxicity in vitro compared with histidine-unmodified polymers. The polyplexes successfully showed PKCα-responsive gene expression immediately after their introduction into cancer cells and the gene expression continued for at least 24 h. These PLL-based carriers thus show promise for cancer-targeted gene therapy.

Design of in silico Trifunctional Antibody (hIgG1-FC: mouse-antiHER2× human-B7.1) Gene Cassettes and Expression Vectors: The Stage Prior to Production

The specific gene cassettes and expression vectors for tri-functional antibody (hIgG1-FC: mouse-antiHER2× human-B7.1) were designed in silico. The in silico tri-functional antibody has been derived from human IgG1, human B7.1, and mouse antiHER2 antibody. The variable domains of IgG1 framework were substituted by Cha21 (mouseantiHER2 scFV) VH-VL, and B7.1 IgV-like domains. The domain data of human IgG1 heavy and light chain-constant regions, human B7.1 IgV-like, and cha21 variable regions were obtained from UniprtoKB and PDB databases. The 3D structure of domains was trimmed and modeled by pyMol software. To ensure the presence of antigen binding residues, complementarity determining regions, and framework regions in variable domain structure, the researchers analyzed the cha21-VH and VL nucleotide sequences using Paratome and IMGT softwares, respectively. In this study, two in silico expression vectors were designed. The vector forms were ready in silico to be synthesized and transfected into CHO cells in order to be developed; the cells expressing the chimeric tri-functional antibody which enables the eradication of HER2-expressing cancer cells using apoptotic induction, T-cell activation and accessory cell activation by antiHER2, B7.1, and Fc domains, respectively.

Construction of an adenoviral expression vector carrying FLAG and hrGFP-1 genes and its expression in bone marrow mesenchymal stem cells

The aim of this study was to construct an adenoviral expression vector for vascular endothelium growth factor 121 (VEGF121)-FLAG and humanized Renilla reniformis green fluorescent protein (hrGFP-1) genes, and to observe their expressions in bone marrow mesenchymal stem cells. Using pTG19T-VEGF121 as a template, polymerase chain reaction technology was adopted to mutate the VEGF121 gene by removing the stop codon and inserting NotI and XhoI restriction sites both before and after the gene sequences. The resultant gene was then subcloned into a pMD19-T plasmid, the pMD19-T-VEGF121 and pShuttle-CMV-IRES-hrGFP-1 plasmids were double-digested, and small and large fragments were linked after gel recovery to complete the construction of recombinant adenovirus vectors. After titer determination, the recombinant adenovirus vectors were used to affect rabbit bone marrow mesenchymal stem cells, and fluorescence intensity was observed under fluorescence microscopy. Enzyme digestion identification and sequencing confirmed that the recombinant plasmids were successfully constructed, and observations under fluorescence microscopy showed significant expression of green fluorescent protein in recombinant adenovirus-infected bone marrow mesenchymal stem cells. The constructed adenoviral gene expression vectors carrying VEGF121-FLAG and hrGFP-1 can be expressed in eukaryotic cells, which may be used for gene therapy of ischemic disorders.

DEVELOPMENT OF DOUBLE GENE MAMMALIAN EXPRESSION VECTOR

Recombinant vectors are valuable tools in the biopharmaceutical industry with a number of novel vectors being developed every day. These Antibodies are often expressed in mammalian cells by cotransfecting light chain and heavy chain containing plasmids. However, co-transfection can lead to variable in the copy number of both heavy chain and light chain, there by affecting the protein productivity. Double gene expression vectors can overcome these problems. In the current design The first transcriptional unit comprises sequences for the CMV promoter, multiple cloning site (MCS) and a Polyadenylation Sequence and the second transcriptional unit comprises sequences for the SV40 promoter, MCS and polyadenylation sequence. The double gene expression vector (pUB-C-S) was constructed by ligating the BglII and BamHI fragment (974bp) form pSI plasmid with BglII digested pCI plasmid. The presence of two independent transcriptional units in the recombinant plasmid was confirmed by colony PCR.

Inhibiting effect of CaMKIIN up-regulation on leukemia cells growth and its mechanism

To investigate the inhibitory effects of CaMKIIN on acute myeloid leukemia cell line HL-60 to explore a novel therapeutic target of leukemia. Human CaMK II N gene expression vector pcDNA3.1/hCaMKIIN or empty vector pcDNA3.1/myc-His (-) B was transfected into HL-60 cells by Lipofectamine 2000. Human CaMK II N proteins of transfected cells were detected by Western blot. Cell proliferation affected by human CaMKIIN was determined by MTT. Colony-forming assay was performed by soft agar growth system. The cells transfected with CaMKIIN were stained with Hoechst 33342 to detect the apoptotic proportion under fluorescence microscopy. Cell cycle was analyzed by flow cytometry. Human CaMKIIN was stably transfected into HL-60 cells, and overexpression of human CaMKIIN inhibited the proliferation of HL-60/CaMKIIN cells compared to HL-60/mock cells and HL-60 cells [(0.44 ± 0.03) vs (0.94 ± 0.05) vs (0.94 ± 0.04), P<0.01]. The colony formation of HL-60/CaMKIIN was also markedly smaller[(21.00 ± 3.05)/500] than that of mock-transfected [(111.00±4.58)/500]] and control cells [(119.00±6.09)/500] (P<0.01). After 72 hrs-culture, the apoptotic proportion in cells transfected with CaMK II N was obviously higher than of cells transfected with mock DNA or control [(22.49 ± 2.15)% vs (7.17 ± 0.72)% vs (6.40 ± 0.55)%, P<0.01]. Up to (82.97 ± 2.90)% human CaMKIIN/HL-60 cells were arrested at G0/G1 phase, which was more than mock-transfected [(40.53 ± 2.38)%] and control cells [(41.63 ± 2.27)%] (P<0.05). Human CaMKIIN could down-regulate expression of Bcl-2 in transfected cells. CaMK IIN up-regulation could inhibit proliferation and induce apoptosis of human acute myeloid leukemia cell HL-60.

Baculoviruses: Sophisticated Pathogens of Insects

The baculoviruses (family: Baculoviridae) are a group of large DNA viruses that infect insects. These viruses are well known for their utility and versatility as gene expression vectors, biological pesticides, and vectors for transduction of mammalian cells [1]–[3]. However, baculoviruses are much more than just useful laboratory tools. The rich and fascinating biology associated with these viruses provides many interesting examples of virus-host interactions and virus modification of host processes. While a few known baculoviruses infect larval mosquitoes or sawflies, the large majority of them infect caterpillars, the larval stages of insects from the order Lepidoptera (moths and butterflies). Baculoviruses typically have narrow host ranges, often limited to just one or a few related insect species, although the most intensely studied member of the family, Autographa californica multiple nucleopolyhedrovirus (AcMNPV), is able to infect as many as 30 species from several lepidopteran genera. Baculovirus nucleocapsids are rod-shaped and surrounded by an envelope, and they contain circular genomes of double-stranded DNA that range in size from about 80–180 kbp in length. Similar to other large DNA viruses, baculoviruses encode numerous accessory genes with roles in manipulating cellular processes such as the cell cycle and apoptosis [4], [5], as well as host physiology and behavior (see below). However, an unusual feature of baculoviruses is that they produce two distinct types of enveloped virions: occlusion-derived virions (ODV), which are embedded in large (5–10 micron) protein crystals called occlusion bodies and are responsible for horizontal transmission between insects, and budded virions (BV), which spread infection from cell to cell (Figure 1). Furthermore, baculoviruses are the only known nuclear-replicating DNA viruses that encode a DNA-directed RNA polymerase, which is used to transcribe the viral late and very late genes, and is also utilized to express foreign genes in the baculovirus expression vector system. Here, we discuss some recent and exciting developments in the baculovirus field; for a comprehensive review of baculoviruses, see [6]. Figure 1 A typical baculovirus replication cycle.

Reciprocal regulation between C/EBP-a and the cellular circadian clock

Objective To study the relationship between CCAAT/enhancer-binding proteins(C/EBPs) and circadian genes expression in mammals. Methods C/EBP-a 240, 280, 650, 1300 and Rev erb-a promoter-luciferase reporter gene expression vectors were set up, as well as the corresponding report gene stable transfection cell lines were established. The intensity and/or rhythm of report gene expression were observed by testing the biological fluorescent. Results The transcription factor CLOCK/BMAL1 heterodimer activated C/EBP-a via a conserved E-box element in its promoter, and the latter showed circadian oscillation which was E-box dependent. On the other hand, C/EBP-a suppressed Rev-erba transcription. Moreover, GR signaling, a known resetting signal for circadian clock, suppressed C/EBP-a transcription. Conclusion The data highlight the reciprocal feedback regulation between a key transcription factor C/EBP-a and the timing mechanism in cells. Key words: Circadian clock; C/EBP-a; E-box; Rev-erba; Bioluminescence assay