Chloramphenicol Acetyltransferase Research Articles

HSV-1 stimulation-related protein HSRG1 inhibits viral gene transcriptional elongation by interacting with Cyclin T2

The protein encoded by HSRG1 (HSV-1 stimulation-related gene 1) is a virally induced protein expressed in HSV-1-infected cells. We have already reported that HSRG1 is capable of interacting with transcriptional regulator proteins. To further analyze the effects of HSRG1 on the regulation of viral gene transcription, we expressed the HSRG1 protein in transfected cells and found that it postpones the proliferation of HSV-1. CAT (chloramphenicol acetyltransferase) assays also revealed that HSRG1 reduces transcription from HSV-1 promoters. Yeast two-hybrid and immunoprecipitation assays indicated that HSRG1 interacts with Cyclin T2, the regulatory subunit of P-TEFb, which is required for transcription elongation by RNA Pol II (RNAP II), and that amino acid residues 1-420 in Cyclin T2 are important for binding with HSRG1. Fluorescence assays suggested that the cellular localizations of those two proteins are influenced by their interaction. Further analyses with CAT assays revealed that HSRG1 inhibits the transcriptional activation by Cyclin T2 of viral promoters. Our results suggested that the inhibitory effects of HSRG1 on viral replication and proliferation are probably induced by its binding to Cyclin T2. Therefore, it is likely that HSRG1 inhibits viral gene transcriptional elongation by interacting with Cyclin T2.

Polymerase Chain Reaction Coupling with Magnetic Nanoparticles-Based Biotin–Avidin System for Amplification of Chemiluminescent Detection Signals of Nucleic Acid

A novel method was established through the detection of chemiluminescent signals of nucleic acid hybridization based on magnetic nanoparticles (MNPs) and PCR. 5' amino- modified specific probes were immobilized on the surface of silanized MNPs by Schiff reaction between amino and aldehyde group. The probes were used to capture the synthetic biotin-dUTP-labeled DNA fragments which were obtained by polymerase chain reaction (PCR). Then these complexes were bonded with streptavidin-modified alkaline phosphatase (SA-AP). Finally the chemiluminescent signals were detected by adding 3-(2'-spiroadamantane)- 4-methoxy -4-(3"-phosphoryloxy) phenyl-1, 2-dioxetane (AMPPD) which was the substrate reagent of AP. The concentration of probes which were immobilized on the surface of MNPs was studied, how to reduce the adsorption of SA-AP on the surface of MNPs was also researched. It was shown that 12.5 pmol of probes were immobilized on 1 mg of MNPs. Aldehyde-MNPs modified with probes could adsorb SA-AP, affecting the sensitivity of chemiluminescene consequently. Reduction of aldehyde group by sodium borohydride and blocking the bare position of MNPs with bovine serum albumin (BSA) could decrease the background of chemiluminescence, and this method has good specificity in detection of chloramphenicol acetyltransferase (CAT) gene.

LuxS Coexpression Enhances Yields of Recombinant Proteins in Escherichia coli in Part through Posttranscriptional Control of GroEL

Cell-to-cell communication, or quorum sensing (QS), enables cell density-dependent regulation of bacterial gene expression which can be exploited for the autonomous-signal-guided expression of recombinant proteins (C. Y. Tsao, S. Hooshangi, H. C. Wu, J. J. Valdes, and W. E. Bentley, Metab. Eng. 12:291-297, 2010). Earlier observations that the metabolic potential of Escherichia coli is conveyed via the QS signaling molecule autoinducer-2 (AI-2) suggested that the capacity for protein synthesis could also be affected by AI-2 signaling (M. P. DeLisa, J. J. Valdes, and W. E. Bentley, J. Bacteriol. 183:2918-2928, 2001). In this work, we found that simply adding conditioned medium containing high levels of AI-2 at the same time as inducing the synthesis of recombinant proteins doubled the yield of active product. We have hypothesized that AI-2 signaling "conditions" cells as a natural consequence of cell-to-cell communication and that this could tweak the signal transduction cascade to alter the protein synthesis landscape. We inserted luxS (AI-2 synthase) into vectors which cosynthesized proteins of interest (organophosphorus hydrolase [OPH], chloramphenicol acetyltransferase [CAT], or UV-variant green fluorescent protein [GFPuv]) and evaluated the protein expression in luxS-deficient hosts. In this way, we altered the level of luxS in the cells in order to "tune" the synthesis of AI-2. We found conditions in which the protein yield was dramatically increased. Further studies demonstrated coincident upregulation of the chaperone GroEL, which may have facilitated higher yields and is shown for the first time to be positively regulated at the posttranscriptional level by AI-2. This report is the first to demonstrate that the protein synthesis capacity of E. coli can be altered by rewiring quorum sensing circuitry.

Bovine Viral Diarrhea Virus Strain- and Cell Type-Specific Inhibition of Type I Interferon Pathways

The interaction of noncytopathogenic bovine viral diarrhea virus type 1 (BVDV-1ncp) with antigen-presenting cell (APC) subsets is of great interest due to the recent increase in severe acute BVDV outbreaks attributed to this genotype (1, 12, 13). We report the effect of a BVDV-1ncp strain (Ho916ncp [13]) causing severe acute infection on in vitro type I interferon (alpha/beta interferon [IFN-α/β]) production compared to that of a mild-acute strain (Ky1203ncp) (15). Ho916ncp but not Ky1203ncp induced IFN-α/β in only lineage-negative (LIN−) cells, a recently described enriched IFN-α/β-producing cell population in cattle (A. Gibson, S. Miah, P. Griebel, J. Brownlie, and D. Werling, submitted for publication). In agreement with published data, monocytes and monocyte-derived dendritic cells (moDC) did not produce IFN-α/β in response to either strain (4, 11, 17). Experimental infection of calves with BVDVncp results in the detection of IFN-α/β and the IFN-α/β-inducible gene Mx (5, 20) as well as serum IFN-α/β activity in pregnant dams and the fetus (22). The identification of IFN-α/β-producing cells within the lymph nodes of BVDVncp-infected calves (4) and of enriched circulating IFN-α/β-producing cells (Gibson et al., submitted) points to an APC subset as a cellular source of IFN-α/β during in vivo BVDVncp infections. In the present study, monocytes, moDC, and LIN− cells, generated from the same animal (11, 24-26, 28; Gibson et al., submitted), were exposed to either strain at a multiplicity of infection (MOI) of 0.1 and IFN-α/β was assessed after 48 h, using a previously described Mx-CAT (chloramphenicol acetyltransferase) reporter assay (4-6, 9). LIN− cells, but not monocytes or moDC, produced significant amounts of IFN-α/β in response to Ho916ncp but not to Ky1203ncp or mock-infected control (Fig. ​(Fig.1).1). To assess whether these observed differences in IFN-α/β production were due to differences in viral replication, the presence of BVDV was determined by immunoperoxidase staining using a bovine hyperimmune serum, similar to what was described previously (11). Astonishingly, no clear differences in abilities to infect the different cell types were seen for the two BVDVncp strains (Fig. ​(Fig.2).2). As differences in viral replication did not explain differences in IFN-α/β production, we next assessed the potential effects of both BVDVncp strains on interferon response factors (IRFs). BVDVncp is known to inhibit IFN-α/β production through viral proteins Npro (2, 3, 10, 14) and Erns (16, 18, 19), which block IFN-α/β production by targeting IRF-3 for degradation by polyubiquitination (7, 14) or by degrading viral RNA (19). Translocation of IRF-3 occurs during infection but not binding to DNA (2). In contrast, IRF-7 is neither activated nor translocated to the nucleus (2). FIG. 1. Type I interferon response to BVDVncp. Monocytes (MON), moDC, and LIN− cells (LIN) were isolated from the same animal and stimulated with 50 μg ml−1 of poly(I:C), BVDVncp strains Ho916ncp and Ky1203ncp at an MOI of 0.1, and corresponding ... FIG. 2. Antigen-presenting cell susceptibility to BVDVncp. Monocytes (A), moDC (B), and LIN− cells (C) were infected with BVDVncp strains Ho916ncp and Ky1203ncp for 48 h (MOI, 0.1). Cells were fixed and stained for the presence of BVDV antigen using a ... We assessed the impact of both strains on IFN-α/β signaling components IRF-3 and IRF-7 by Western blotting, which showed that IRF-3 and IRF-7 were increased in all three cell types infected with Ho916ncp compared to mock-infected controls. In contrast, Ky1203ncp induced a reduction of IRF-7 expression in monocytes and moDC and a reduction in IRF-3 expression in all three cell types. IRF-7 remained unchanged in LIN− cells, potentially indicating cell type-specific degradation in monocytes and moDC for Ky1203ncp (Fig. ​(Fig.3).3). Ho916ncp-induced IFN-α/β production by LIN− cells appears to be independent of IRF-3 or IRF-7 modulation; however, LIN− cells, unlike monocytes or moDC, express TLR7 (27; Gibson et al., submitted), which has been recently implicated in the recognition of other pestiviruses, such as West Nile virus and dengue virus (8, 21, 23). Ho916ncp, as a severe acute BVDV-1ncp strain could be more readily accessible to the endosomal compartment within LIN− cells, thus producing cell type-restricted IFN-α/β through TLR7. Our data show for the first time differences in BVDV-1ncp strains with regard to a cell-specific IFN-α/β response and offer some suggestions for this modulation. FIG. 3. Relative expression of IRF-3 and IRF-7 in response to BVDVncp. Monocytes (MON), moDC, and LIN− (LIN) cells were isolated from the same animal and stimulated with Ho916ncp and Ky1203ncp alongside mock-infected controls for 48 h. Protein lysates ...

A functional tetranucleotide (AAAT) polymorphism in an Alu element in the NF1 gene is associated with mental retardation

Mental retardation (MR) is frequent in neurofibromatosis type 1 (NF1). Allele 5 of a tetranucleotide polymorphism in an Alu element (GXAlu) localized in intron 27b of the NF1 gene has previously been associated with autism. We considered that the microsatellite GXAlu could also represent a risk factor in MR without autism. We developed a rapid method for genotyping by non-denaturing HPLC and assayed the allelic variation of GXAlu marker on in vitro gene expression in Cos-7 cells. A French population of 157 individuals (68 non syndromic non familial MR (NS-MR) patients diagnosed in the University Hospital of Tours; 89 controls) was tested in a case-control assay. We observed a significant association ( χ 2 = 7.96; p = 0.005) between alu4 carriers (7 AAAT repeats) and MR (OR: 7.86; 95% C.I.: 2.13–28.9). The relative in vitro expression of a reporter gene encoding chloramphenicol acetyl transferase (CAT) was higher for alu4 and alu5, suggesting a regulation effect for these alleles on gene expression in vivo. Our results showed an association with a polymorphism regulating the NF1 gene or other genes during brain development.

A new inducible expression system in a transformed green alga, Chlorella vulgaris

Genetic transformation is useful for basic research and applied biotechnology. However, genetic transformation of microalgae is usually quite difficult due to the technical limitations of existing methods. We cloned the promoter and terminator of the nitrate reductase gene from the microalga Phaeodactylum tricornutum and used them for optimization of a transformation system of the microalga Chlorella vulgaris. This species has been used for food production and is a promising candidate as a bioreactor for large-scale production of value-added proteins. A construct was made containing the CAT (chloramphenicol acetyltransferase) reporter gene driven by the nitrate reductase promoter. This construct was transferred into the C. vulgaris genome by electroporation. Expression of CAT in transgenic Chlorella conferred resistance to the antibiotic chloramphenicol and enabled growth in selective media. Overall efficiency for the transformation was estimated to be approximately 0.03%, which is relatively high compared with other available Chlorella transformation systems. Expression of CAT was induced in the presence of nitrate and inhibited in the presence of ammonium as a sole nitrogen source. This study presented an inducible recombinant gene expression system, also providing more gene regulation elements with potential for biotechnological applications.

Identification and Characterization of Novel and Potent Transcription Promoters of Francisella tularensis

Two alternative promoter trap libraries, based on the green fluorescence protein (gfp) reporter and on the chloramphenicol acetyltransferase (cat) cassette, were constructed for isolation of potent Francisella tularensis promoters. Of the 26,000 F. tularensis strain LVS gfp library clones, only 3 exhibited visible fluorescence following UV illumination and all appeared to carry the bacterioferritin promoter (Pbfr). Out of a total of 2,000 chloramphenicol-resistant LVS clones isolated from the cat promoter library, we arbitrarily selected 40 for further analysis. Over 80% of these clones carry unique F. tularensis DNA sequences which appear to drive a wide range of protein expression, as determined by specific chloramphenicol acetyltransferase (CAT) Western dot blot and enzymatic assays. The DNA sequence information for the 33 unique and novel F. tularensis promoters reported here, along with the results of in silico and primer extension analyses, suggest that F. tularensis possesses classical Escherichia coli σ(70)-related promoter motifs. These motifs include the -10 (TATAAT) and -35 [TTGA(C/T)A] domains and an AT-rich region upstream from -35, reminiscent of but distinct from the E. coli upstream region that is termed the UP element. The most efficient promoter identified (Pbfr) appears to be about 10 times more potent than the F. tularensis groEL promoter and is probably among the strongest promoters in F. tularensis. The battery of promoters identified in this work will be useful, among other things, for genetic manipulation in the background of F. tularensis intended to gain better understanding of the mechanisms involved in pathogenesis and virulence, as well as for vaccine development studies.

Evolution of interleukin-15 for higher E. coli expression and solubility

Directed evolution was used to generate IL-15 mutants with increased solubility and cytoplasmic over-expression in Escherichia coli. A protein solubility selection method was used in which the IL-15 gene was expressed as an N-terminal fusion to chloramphenicol acetyltransferase (CAT) as reporter protein. Clones that grew in the presence of high concentrations of chloramphenicol were then screened by ELISA to assay the binding activity of the IL-15-CAT fusion to the IL-15Rα Sushi domain. Two variants of IL-15, M38 and M253, containing five mutations and one mutation respectively, were selected with a dramatic improvement in solubility; the soluble concentration in cell culture was 12- to 18-fold higher, respectively, than for WT IL-15. Characterization of their binding to IL-15Rα and their ability to stimulate the T-cell growth response showed that M38 binds as strongly as native IL-15 to IL-15Rα and acts as an effective agonist of IL-15.

Whole-Genome Analysis of Salmonella enterica Serovar Typhimurium T000240 Reveals the Acquisition of a Genomic Island Involved in Multidrug Resistance via IS 1 Derivatives on the Chromosome

Salmonella enterica serovar Typhimurium is frequently associated with life-threatening systemic infections, and the recent global emergence of multidrug resistance in S. enterica isolates from agricultural and clinical settings has raised concerns. In this study, we determined the whole-genome sequence of fluoroquinolone-resistant S. enterica serovar Typhimurium T000240 strain (DT12) isolated from human gastroenteritis in 2000. Comparative genome analysis revealed that T000240 displays high sequence similarity to strain LT2, which was originally isolated in 1940, indicating that progeny of LT2 might be reemerging. T000240 possesses a unique 82-kb genomic island, designated as GI-DT12, which is composed of multidrug resistance determinants, including a Tn2670-like composite transposon (class 1 integron [intI1, bla(oxa-30), aadA1, qacEΔ1, and sul1], mercury resistance proteins, and chloramphenicol acetyltransferase), a Tn10-like tetracycline resistance protein (tetA), the aerobactin iron-acquisition siderophore system (lutA and lucABC), and an iron transporter (sitABCD). Since GI-DT12 is flanked by IS1 derivatives, IS1-mediated recombination likely played a role in the acquisition of this genomic island through horizontal gene transfer. The aminoglycoside-(3)-N-acetyltransferase (aac(3)) gene and a class 1 integron harboring the dfrA1 gene cassette responsible for gentamicin and trimethoprim resistance, respectively, were identified on plasmid pSTMDT12_L and appeared to have been acquired through homologous recombination with IS26. This study represents the first characterization of the unique genomic island GI-DT12 that appears to be associated with possible IS1-mediated recombination in S. enterica serovar Typhimurium. It is expected that future whole-genome studies will aid in the characterization of the horizontal gene transfer events for the emerging S. enterica serovar Typhimurium strains.

Effects of neurosteroids on the human corticotropin-releasing hormone gene

Increased activity of hypothalamic-pituitary-adrenal (HPA) axis and hypersecretion of corticotropin-releasing hormone (CRH) are known to be important factors in pathogenesis of some stress-related diseases. Some neurosteroids exert anxiolytic and antidepressant effects probably by inhibition of HPA axis activity. The aim of our study was to find out if neurosteroids can directly affect human CRH gene transcription. The effect of allopregnanolone (ALLO), allotetrahydrodeoxycorticosterone (THDOC), pregnenolone (PGL), PGL sulfate (PGL-S), dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEA-S) on CRH expression was determined in differentiated Neuro-2A cells stably transfected with plasmid containing a fragment of human CRH promoter (-663 to+124bp) linked to the chloramphenicol acetyltransferase (CAT) reporter gene. It was found that PGL (0.3–30μΜ), ALLO (1–30μΜ) and THDOC (1–30μΜ) present in the culture medium for 5 days in the concentration-dependent manner inhibited CRH-CAT activity. These neurosteroids also inhibited forskolin-stimulated CRH gene transcription with similar potency. In contrast, PGL-S, DHEA and DHEA-S in a concentration from 0.01 to 10μΜ had no effect on basal and forskolin-stimulated CRH activity. Further experiments revealed that wortmannin (an inhibitor of phosphatidylinositol 3-kinase; PI3-K) at concentrations of 0.01 and 0.02μΜ did not change the inhibitory effect of ALLO (3μΜ) and PGL (1μΜ) on CRH gene transcription. Moreover, ALLO (3μΜ) and PGL (1μΜ) present in the culture medium for 5 days did not change the amount of active, phosphorylated form of protein kinase B (PKB, Akt) and extracellular signal-regulated kinase (ERK). The obtained results indicate that PGL, ALLO and THDOC inhibited basal and forskolin-induced CRH gene promoter activity in the differentiated Neuro-2A cells and that these effects did not depend on the activation of PI3-K/Akt and ERK-MAPK pathways.

Proteasome Inhibitors Enhance Gene Delivery by AAV Virus Vectors Expressing Large Genomes in Hemophilia Mouse and Dog Models: A Strategy for Broad Clinical Application

Delivery of genes that are larger than the wild-type adeno-associated virus (AAV) 4,681 nucleotide genome is inefficient using AAV vectors. We previously demonstrated in vitro that concurrent proteasome inhibitor (PI) treatment improves transduction by AAV vectors encoding oversized transgenes. In this study, an AAV vector with a 5.6 kilobase (kb) factor VIII expression cassette was used to test the effect of an US Food and Drug Administration-approved PI (bortezomib) treatment concurrent with vector delivery in vivo. Intrahepatic vector delivery resulted in factor VIII expression that persisted for >1 year in hemophilia mice. Single-dose bortezomib given with AAV2 or AAV8 factor VIII vector enhanced expression on average ~600 and ~300%, respectively. Moreover, coadministration of AAV8.canineFVIII (1 × 10(13) vg/kg) and bortezomib in hemophilia A dogs (n = 4) resulted in normalization of the whole blood clotting time (WBCT) and 90% reduction in hemorrhages for >32 months compared to untreated hemophilia A dogs (n = 3) or dogs administered vector alone (n = 3). Demonstration of long-term phenotypic correction of hemophilia A dogs with combination adjuvant bortezomib and AAV vector expressing the oversized transgene establishes preclinical studies that support testing in humans and provides a working paradigm to facilitate a significant expansion of therapeutic targets for human gene therapy.

Proteasomal Degradation Is Transcriptionally Controlled by TCF11 via an ERAD-Dependent Feedback Loop

Coordinated regulation of the ubiquitin-proteasome system (UPS) is crucial for the cell to adjust its protein degradation capacity to changing proteolytic requirements. We have shown previously that mammalian cells upregulate proteasome gene expression in response to proteasome inhibition. Here, we report the identification of the transcription factor TCF11 (long isoform of Nrf1) as a key regulator for 26S proteasome formation in human cells to compensate for reduced proteolytic activity. Under noninducing conditions, TCF11 resides in the endoplasmic reticulum (ER) membrane. There, TCF11 is targeted to ER-associated protein degradation requiring the E3 ubiquitin ligase HRD1 and the AAA ATPase p97. Proteasome inhibitors trigger the accumulation of oxidant-damaged proteins and promote the nuclear translocation of TCF11 from the ER, permitting activation of proteasome gene expression by binding to antioxidant response elements in their promoter regions. Thus, we uncovered the transcriptional control loop regulating human proteasome-dependent protein degradation to counteract proteotoxic stress caused by proteasome inhibition.

Pax6 Controls the Expression of Critical Genes Involved in Pancreatic α Cell Differentiation and Function*

The paired box homeodomain Pax6 is crucial for endocrine cell development and function and plays an essential role in glucose homeostasis. Indeed, mutations of Pax6 are associated with diabetic phenotype. Importantly, homozygous mutant mice for Pax6 are characterized by markedly decreased β and δ cells and absent α cells. To better understand the critical role that Pax6 exerts in glucagon-producing cells, we developed a model of primary rat α cells. To study the transcriptional network of Pax6 in adult and differentiated α cells, we generated Pax6-deficient primary rat α cells and glucagon-producing cells, using either specific siRNA or cells expressing constitutively a dominant-negative form of Pax6. In primary rat α cells, we confirm that Pax6 controls the transcription of the Proglucagon and processing enzyme PC2 genes and identify three new target genes coding for MafB, cMaf, and NeuroD1/Beta2, which are all critical for Glucagon gene transcription and α cell differentiation. Furthermore, we demonstrate that Pax6 directly binds and activates the promoter region of the three genes through specific binding sites and that constitutive expression of a dominant-negative form of Pax6 in glucagon-producing cells (InR1G9) inhibits the activities of the promoters. Finally our results suggest that the critical role of Pax6 action on α cell differentiation is independent of those of Arx and Foxa2, two transcription factors that are necessary for α cell development. We conclude that Pax6 is critical for α cell function and differentiation through the transcriptional control of key genes involved in glucagon gene transcription, proglucagon processing, and α cell differentiation.

Facile synthesis of metal-chelating magnetic nanoparticles by exploiting organophosphorus coupling

A new method is described for facile synthesis of metal-chelating magnetic nanoparticles by simply mixing iron oxide nanoparticles with a bifunctional organophosphorus compound, N-(phosphonomethyl)iminodiacetic acid (PM–IDA), in aqueous solution. On charging with nickel ions, the PM–IDA functionalized iron oxide nanoparticles exhibited high His-tag protein binding capacity (0.21 and 0.58 mg/mg for His-tagged green fluorescent protein and chloramphenicol acetyltransferase, respectively) and were successfully used to purify these proteins from bacterial cell extracts to high purity in a single step. Although other synthetic schemes for metal-chelating magnetic nanoparticles have been reported, the method described here is markedly simpler and involves only low-cost reagents.

Enhanced Production of l-Arginine by Expression of Vitreoscilla Hemoglobin Using a Novel Expression System in Corynebacterium crenatum

Corynebacterium crenatum SYPA 5-5 is an aerobic and industrial L: -arginine producer. It was proved that the Corynebacterium glutamicum/Escherichia coli shuttle vector pJC1 could be extended in C. crenatum efficiently when using the chloramphenicol acetyltransferase gene (cat) as a reporter under the control of promoter tac. The expression system was applied to over-express the gene vgb coding Vitreoscilla hemoglobin (VHb) to further increase the dissolved oxygen in C. crenatum. As a result, the recombinant C. crenatum containing the pJC-tac-vgb plasmid expressed VHb at a level of 3.4 nmol g(-1), and the oxygen uptake rates reached 0.25 mg A(562)(-1) h(-1) which enhanced 38.8% compared to the wild-type strain. Thus, the final L: -arginine concentration of the batch fermentation reached a high level of 35.9 g L(-1), and the biomass was largely increased to 6.45 g L(-1), which were 17.3% and 10.5% higher than those obtained by the wild-type strain, respectively. To our knowledge, this is the first report that the efficient expression system was constructed to introduce vgb gene increasing the oxygen and energy supply for L: -arginine production in C. crenatum, which supplies a good strategy for the improvement of amino acid products.

HIV-1 Reactivation Induced by the Periodontal Pathogens Fusobacterium nucleatum and Porphyromonas gingivalis Involves Toll-Like Receptor 4 and 9 Activation in Monocytes/Macrophages

ABSTRACT Although oral coinfections (e.g., periodontal disease) are highly prevalent in human immunodeficiency virus type 1-positive (HIV-1 + ) patients and appear to positively correlate with viral load levels, the potential for oral bacteria to induce HIV-1 reactivation in latently infected cells has received little attention. We showed that HIV-1 long terminal repeat (LTR) promoter activation can be induced by periodontopathogens in monocytes/macrophages; nevertheless, the mechanisms involved in this response remain undetermined. Since Toll-like receptor 2 (TLR2), TLR4, and TLR9 activation have been involved in HIV-1 recrudescence, we sought to determine the role of these TLRs in HIV-1 reactivation induced by the periodontal pathogens Fusobacterium nucleatum and Porphyromonas gingivalis using BF24 monocytes/macrophages stably transfected with the HIV-1 promoter driving chloramphenicol acetyltransferase (CAT) expression and THP89GFP cells, a model of HIV-1 latency. We demonstrated that TLR9 activation by F. nucleatum and TLR2 activation by both bacteria appear to be involved in HIV-1 reactivation; however, TLR4 activation had no effect. Moreover, the autocrine activity of tumor necrosis factor alpha (TNF-α) but not interleukin-1β (IL-1β) produced in response to bacteria could impact viral reactivation. The transcription factors NF-κB and Sp1 appear to be positively regulating HIV-1 reactivation induced by these oral pathogens. These results suggest that oral Gram-negative bacteria ( F. nucleatum and P. gingivalis ) associated with oral and systemic chronic inflammatory disorders enhance HIV-1 reactivation in monocytes/macrophages through TLR2 and TLR9 activation in a mechanism that appears to be transcriptionally regulated. Increased bacterial growth and emergence of these bacteria or their products accompanying chronic oral inflammatory diseases could be risk modifiers for viral replication, systemic immune activation, and AIDS progression in HIV-1 + patients.

Chloramphenicol acetyltransferase as selectable marker for plastid transformation

Chloroplast transformation remains a demanding technique and is still restricted to relatively few plant species. The limited availability of selectable marker genes and the lack of selection markers that would be universally applicable to all plant species represent some of the most serious technical problems involved in extending the species range of plastid transformation. Here we report the development of the chloramphenicol acetyltransferase gene cat as a new selectable marker for plastid transformation. We show that, by selecting for chloramphenicol resistance, tobacco chloroplast transformants are readily obtained. Transplastomic lines quickly reach the homoplasmic state (typically in one additional regeneration round), accumulate the chloramphenicol acetyltransferase enzyme to high levels and transmit their plastid transgenes maternally into the next generation. No spontaneous antibiotic resistance mutants appear upon chloramphenicol selection. Several lines of evidence support the assumption that plant mitochondria are also sensitive to chloramphenicol suggesting that the chloramphenicol acetyltransferase may be a good candidate selectable marker for plant mitochondrial transformation.

Diversity and strength of internal outward-oriented promoters in group IIC-attC introns

Integrons are genetic elements that incorporate mobile gene cassettes by site-specific recombination and express them as an operon from a promoter (Pc) located upstream of the cassette insertion site. Most gene cassettes found in integrons contain only one gene followed by an attC recombination site. We have recently shown that a specific lineage of group IIC introns, named group IIC-attC introns, inserts into the bottom strand sequence of attC sites. Here, we show that S.ma.I2, a group IIC-attC intron inserted in an integron cassette array of Serratia marcescens, impedes transcription from Pc while allowing expression of the following antibiotic resistance cassette using an internal outward-oriented promoter (Pout). Bioinformatic analyses indicate that one or two putative Pout, which have sequence similarities with the Escherichia coli consensus promoters, are conserved in most group IIC-attC intron sequences. We show that Pout with different versions of the −35 and −10 sequences are functionally active in expressing a promoterless chloramphenicol acetyltransferase (cat) reporter gene in E. coli. Pout in group IIC-attC introns may therefore play a role in the expression of one or more gene cassettes whose transcription from Pc would otherwise be impeded by insertion of the intron.

Screening and application of prokaryotic enhancer-like sequence 3A

To screen enhancer-like sequences from Escherichia coli strain C600 genome, to construct an expression vector harboring prokaryotic enhancer-like sequence and study the effect of interferon gene expression. Enhancer-like element from Escherichia coli strain C600 genome was obtained by using the chloramphenicol acetyl-transferase (CAT) gene as reporter gene. An expression vector harboring prokaryotic enhancer-like sequence from Escherichia coli strain C600 was constructed. Interferon was expressed and assayed. An enhancer-like sequences with distance and orientation independence property were screened and named 3A. Quantification test showed that the direct and reverse orientation of 3A could increase the activity of beta-galactosidase with 7.11 and 2.93 times. The enhancing activity of the element was on transcription level. An expression vector harboring the prokaryotic enhancer-like sequence 3P3 which was enhancing function region of sequence 3A was constructed. Using this vector the antiviral activity of interferon alpha-2b was increased by 3.7 times in comparison with the original expression plasmid. 3A enhancer-like sequence was screened from Escherichia coli strain C600 genome. Interferon gene was highly expressed by using an expression vector harboring enhancer-like sequences.

Herpes simplex virus type 1 tegument protein VP22 is capable of modulating the transcription of viral TK and gC genes via interaction with viral ICP0

VP22, a tegument protein of herpes simplex virus type 1 (HSV-1), is present in many copies in one virion and undergoes different types of post-translational modification. VP22 is believed to have certain functions in viral infection apart from virus assembly. Here we show that VP22 physically interacted with infected cell polypeptide 0 (ICP0) and colocalized in the nucleus, indicating that VP22 could be functionally involved in the modulation of viral transcription through interaction with ICP0. In the HSV-1 infection system and chloramphenicol acetyltransferase (CAT) transcriptional system, VP22–ICP0 interaction was confirmed to play a role in modulating the transcription of some viral genes and could be a factor in viral transcription, which is probably required in the transcriptional control of latent infection.