Improved Transient Protein Expression by pFluNS1 Plasmid

Influenza virus nonstructural protein-1 (NS1) is abundantly expressed in influenza virus infected cells. NS1 is well recognized for counteracting host antiviral activities and regulating host and viral protein expression. When used as a plasmid component in DNA transfection, NS1 was shown to significantly increase expression levels of a cotransfected gene of different plasmid. Our previous studies demonstrated that addition of an NS1 plasmid increased the expression levels of influenza virus secreted neuraminidase (sNA) gene in 293T cells. In this study, we improved the utilization of NS1 as an enhancer for transient protein expression by generating pFluNS1 plasmid to contain two expression cassettes; one encoding an NS1 gene and another encoding a gene of interest. pFluNS1 is expected to codeliver the NS1 gene into the same cells receiving the gene of interest. The plasmid is therefore designed to induce higher protein expression levels than a cotransfection of an NS1 plasmid and a plasmid containing a gene of interest. To test the efficiency of pFluNS1, influenza virus sNA and non-viral DsRed genes were cloned into pFluNS1. The expression of these genes from pFluNS1 was then compared to the expression from a cotransfection of an NS1 plasmid and an expression plasmid coding for sNA or DsRed. We found that gene expression from pFluNS1 reached equal or higher levels to those derived from the cotransfection. Because the expression from pFluNS1 needs only one plasmid, a lesser amount of transfection reagent was required. Thus, the use of pFluNS1 provides a transfection approach that reduces the cost of protein expression without compromising high levels of protein expression. Together, these data suggest that pFluNS1 can serve as a novel alternative for an efficient transient protein expression in mammalian cells.     

Biosynthesis of folic acid

Summary Biosynthesis of folic acid activity by Bacillus subtilis cell suspensions was studied with respect to substrates utilized as precursors. Among purine bases, adenine was utilized the best and not guanine although guanosine or guanylic acid were utilized efficiently. Among 3-C precursors, glyceraldehyde gave maximum synthesis of folate activity. The cells appeared to utilize p-aminobenzoate preferentially to p-aminobenzoyl-glutamate. Pteroic acid appears to be an intermediate in the synthesis of folate derivatives in this system. Ascorbic acid stimulates the synthesis to a great extent.     

Cloning of genes specifying carbohydrate catabolism in Pseudomonas aeruginosa and Pseudomonas putida.

A 6.0-kilobase EcoRI fragment of the Pseudomonas aeruginosa PAO chromosome containing a cluster of genes specifying carbohydrate catabolism was cloned into the multicopy plasmid pRO1769. The vector contains a unique EcoRI site for cloning within a streptomycin resistance determinant and a selectable gene encoding gentamicin resistance. Mutants of P. aeruginosa PAO transformed with the chimeric plasmid pRO1816 regained the ability to grow on glucose, and the following deficiencies in enzyme or transport activities corresponding to the specific mutations were complemented: glcT1, glucose transport and periplasmic glucose-binding protein; glcK1, glucokinase; and edd-1, 6-phosphogluconate dehydratase. Two other carbohydrate catabolic markers that are cotransducible with glcT1 and edd-1 were not complemented by plasmid pRO1816: zwf-1, glucose-6-phosphate dehydrogenase; and eda-9001, 2-keto-3-deoxy-6-phosphogluconate aldolase. However, all five of these normally inducible activities were expressed at markedly elevated basal levels when transformed cells of prototrophic strain PAO1 were grown without carbohydrate inducer. Vector plasmid pRO1769 had no effect on the expression of these activities in transformed mutant or wild-type cells. Thus, the chromosomal insert in pRO1816 contains the edd and glcK structural genes, at least one gene (glcT) that is essential for expression of the glucose active transport system, and other loci that regulate the expression of the five clustered carbohydrate catabolic genes. The insert in pRO1816 also complemented the edd-1 mutation in a glucose-negative Pseudomonas putida mutant but not the eda-1 defect in another mutant. Moreover, pRO1816 caused the expression of high specific activities of glucokinase, an enzyme that is naturally lacking in these strains of Pseudomonas putida.     

MiR-22重组腺病毒的构建及对HepG2细胞葡萄糖摄取的影响

文中构建了miR-22重组腺病毒Ad-miR-22,分析了其对HepG2细胞胰岛素信号通路及葡萄糖摄取的抑制作用。通过PCR方法,扩增了miR-22的前体及侧翼序列,酶切后克隆至腺病毒穿梭载体pAdTrack-CMV中,构建穿梭质粒pAdT-22,经PCR及测序鉴定。穿梭质粒经PmeⅠ线性化后,直接转化含有腺病毒骨架载体的感受态细胞BJ5183,产生重组腺病毒质粒Ad-miR-22,最后经PacⅠ线性化后转染包装细胞系293A。重组腺病毒经过3轮扩增后感染HepG2细胞,通过荧光定量PCR检测miR-22表达水平。通过葡萄糖摄取实验观察Ad-miR-22对HepG2细胞葡萄糖摄取的影响。采用Western blotting检测Ad-miR-22对HepG2细胞SIRT1在蛋白质水平的表达及GSK-3β磷酸化水平的影响。采用荧光定量PCR检测miR-22对PEPCK及G6Pase等基因在mRNA水平表达的影响。结果表明,重组腺病毒Ad-miR-22感染显著增加HepG2细胞miR-22表达水平。此外,Ad-miR-22显著抑制胰岛素诱导的HepG2葡萄糖摄取,并通过下调GSK-3β磷酸化抑制胰岛素信号通路的激活。Ad-miR-22反转胰岛素对糖异生关键酶表达的抑制作用,并下调SIRT1基因在蛋白质水平的表达。综上所述,构建了miR-22的重组腺病毒,发现其显著增加糖异生,抑制HepG2细胞葡萄糖摄取,该作用可能与miR-22调节SIRT1在蛋白质水平的表达有关。     

High-level expression of c-H-ras1 fails to fully transform rat-1 cells.

Rat-1 cells were transfected with plasmids encoding normal (Gly-12), nonactivated (Pro-12), and activated (Val-12 and Ile-12) p21H-ras in the presence of an amplifiable dihydrofolate reductase marker. The introduced DNA was amplified by selection in methotrexate to establish the relationship between p21H-ras expression and various hallmarks of cellular transformation. The maximum level of p21H-ras (Gly-12) consistent with cell viability was approximately 0.13% of total cell protein (approximately 60,000 molecules per cell); this is 44-fold greater than the level of the endogenous protein. The maximum tolerated level of a second nontransforming form of p21H-ras (pro-12) was about half of this. Amplification in Rat-1 cells of H-ras genes encoding the highly oncogenic Val-12 and Ile-12 forms of p21H-ras could not be achieved by methotrexate selection, providing strong evidence that synthesis of activated p21H-ras above a certain threshold (about 0.02% of total protein) in Rat-1 cells is incompatible with cell viability. Individual cell lines were isolated and their morphology, anchorage-independent growth, tumorigenicity, and response to and production of growth factors were studied. We report that cell lines expressing near-maximum tolerated levels of either the normal or pro-12 form of p21H-ras were not as transformed as cells expressing much more modest levels of the highly oncogenic (Val-12) form, suggesting that the complete elaboration of the transformed phenotype by ras depends, at least in part, on mutations that distinguish the cellular and viral proteins. We found that cells expressing elevated levels of the normal p21(H-ras) could be fully transformed by the activated (Val-12) form and that such cells continued to overexpress p21(H-ras) (Gly-12), arguing against a role for normal ras genes in suppression of the oncogenic potential of their mutationally activated counterparts.     

Isolation and study of hybrid plasmids carrying Escherichia coli threonine operon genes

A fragment of Escherichia coli chromosome containing the intact threonine operon or its distinct genes has been cloned on the pBR322 plasmid. This fragment has been mapped using some restriction endonucleases. Cloning results in an increased level of appropriate enzyme activity in cells containing hybrid plasmids. Those carrying the complete threonine operon are capable of accumulating threonine up to 5 g/l in culture medium during 48 h. When multi-copy plasmids are used for gene cloning, interpretation of experiments aimed at transformation of auxotrophic bacterial strains, might be complicated. For example, transformation of appropriate threonine auxotrophs by a hybrid plasmid carrying mutation in the threonine gene, might result in prototrophic phenotype. It is possible that the great amount of mutant enzyme molecules compensated their low activity. On the contrary, the presence of a gene within the plasmid, as shown by restriction and biochemical analysis, did not always ensure the growth on a minimal medium of auxotrophs transformed by this plasmid.     

Mechanism of plasmid delivery by hydrodynamic tail vein injection. I. Hepatocyte uptake of various molecules

BACKGROUND: The hydrodynamic tail vein (HTV) injection of naked plasmid DNA is a simple yet effective in vivo gene delivery method into hepatocytes. It is increasingly being used as a research tool to elucidate mechanisms of gene expression and the role of genes and their cognate proteins in the pathogenesis of disease in animal models. A greater understanding of its mechanism will aid these efforts and has relevance to macromolecular and nucleic acid delivery in general. METHODS: In an attempt to explore how naked DNA enters hepatocytes the fate of a variety of molecules and particles was followed over a 24-h time frame using fluorescence microscopy. The uptake of some of these compounds was correlated with marker gene expression from a co-injected plasmid DNA. In addition, the uptake of the injected compounds was correlated with the histologic appearance of hepatocytes. RESULTS: Out of the large number of nucleic acids, peptides, proteins, inert polymers and small molecules that we tested, most were efficiently delivered into hepatocytes independently of their size and charge. Even T7 phage and highly charged DNA/protein complexes of 60-100 nm in size were able to enter the cytoplasm. In animals co-injected with an enhanced yellow fluorescent protein (EYFP) expression vector and fluorescently labeled immunoglobulin (IgG), hepatocytes flooded with large amounts of IgG appeared permanently damaged and did not express EYFP-Nuc. Hepatocytes expressing EYFP had only slight IgG uptake. In contrast, when an EYFP expression vector was co-injected with a fluorescently labeled 200-bp linear DNA fragment, both were mostly (in 91% of the observed cells) co-localized to the same hepatocytes 24 h later. CONCLUSIONS: The appearance of permanently damaged cells with increased uptake of some molecules such as endogenous IgG raised the possibility that a molecule could be present in a hepatocyte but its transport would not be indicative of the transport process that can lead to foreign gene expression. The HTV procedure enables the uptake of a variety of molecules (as previous studies also found), but the uptake process for some of these molecules may be associated with a more disruptive process to the hepatocytes that is not compatible with successful gene delivery.     

Effect of drug transporter genes on cysteine export and overproduction in Escherichia coli

L-cysteine is an important amino acid in terms of its industrial applications. We previously found a marked production of L-cysteine from glucose in recombinant Escherichia coli cells expressing an altered cysE gene encoding feedback inhibition-insensitive serine acetyltransferase. Also, a lower level of cysteine desulfhydrase (CD) activity, which is involved in L-cysteine degradation, increased L-cysteine productivity in E. coli. The use of an L-cysteine efflux system could be promising for breeding L-cysteine overproducers. In addition to YdeD and YfiK, which have been reported previously as L-cysteine exporter proteins in E. coli, we analyzed the effects of 33 putative drug transporter genes in E. coli on L-cysteine export and overproduction. Overexpression of the acrD, acrEF, bcr, cusA, emrAB, emrKY, ybjYZ, and yojIH genes reversed the growth inhibition of tnaA (the major CD gene)-disrupted E. coli cells by L-cysteine. We also found that overexpression of these eight genes reduces intracellular L-cysteine levels after cultivation in the presence of L-cysteine. Amino acid transport assays showed that Bcr overexpression conferring bicyclomycin and tetracycline resistance specifically promotes L-cysteine export driven by energy derived from the proton gradient. When a tnaA-disrupted E. coli strain expressing the altered cysE gene was transformed with a plasmid carrying the bcr gene, the transformant exhibited more L-cysteine production than cells carrying the vector only. A reporter gene assay suggested that the bcr gene is constitutively expressed at a substantial level. These results indicate that the multidrug transporter Bcr in the major facilitator family is involved in L-cysteine export and overproduction in genetically engineered E. coli cells.     

Tyrosine phosphorylation of a 22-kDa protein is correlated with transformation by Rous sarcoma virus

Recent studies from this laboratory have identified novel cytoskeletal proteins that are phosphorylated on tyrosine in vivo in Rous sarcoma virus-transformed chick fibroblasts (Glenney, J. R., Jr., and Zokas, L. (1989) J. Cell Biol. 108, 2401-2408). In the present report, the phosphorylation of these proteins was examined in cells expressing the nonmyristylated mutants of src that are not transformed. A good correlation was found between transformation and the tyrosine phosphorylation of a 22-kDa protein. Tyrosine phosphorylation of the 22-kDa protein was reduced more than 95% in cells expressing the nonmyristylated mutants of src. Size fractionation revealed that the 22-kDa phosphoprotein in transformed chick fibroblasts is found in a Mr 150,000 complex. Monoclonal antibodies were used to screen various chicken tissues where the 22-kDa protein was found at high levels in muscle and lung with low levels in epithelial cells and brain. The 22-kDa protein becomes an excellent candidate for a mediator of transformation by the tyrosine kinase class of oncogenes.     

Biochemical genetics of tryptophan synthesis in Pseudomonas acidovorans.

Sixty independent tryptophan auxotrophs of Pseudomonas acidovorans were isolated and characterized for nutritional response to intermediates of the pathway, accumulation of intermediates, and levels of tryptophan-synthetic enzymes. Mutants for each of the seven proteins catalyzing the five steps of tryptophan synthesis were obtained. Transductional analysis established three unlinked chromosomal regions: trpE, trpGDC, and trpFBA. The order of the genes within the two clusters was not determined. The levels and enzymatic activities of wild-type and mutant strains indicated that trpE and trpGDC were repressed by tryptophan. In contrast, trpFBA was not derepressed significantly by starvation for tryptophan. The trpG mutants had an additional requirement for p-aminobenzoate, which suggested that anthranilate synthase subunit II also served as glutamine-binding protein in the analogous reaction catalyzed by p-aminobenzoate synthase. In addition, trpD mutants revealed the ability of P. acidovorans to degrade anthranilate via the beta-ketoadipate pathway.     

Estimating the number of plasmids taken up by a eukaryotic cell during transfection and evidence that antisense RNA abolishes gene expression in Physarum polycephalum

We have estimated the statistical distribution of the number of plasmids taken up by individual Jurkat lymphoma cells during electroporation in the presence of two plasmids, one encoding for yellow (EYFP) the other for cyan (ECFP) fluorescent protein. The plasmid concentration at which most of the cells take up only one plasmid or several molecules was determined by statistical analysis. We found that cells behaved slightly heterogeneous in plasmid uptake and describe how the homogeneity of a cell population can be quantified by Poisson statistics in order to identify experimental conditions that yield homogeneously transfection-competent cell populations. The experimental procedure worked out with Jurkat cells was applied to assay the effectiveness of antisense RNA in knocking down gene expression in Physarum polycephalum. Double transfection of flagellates with vectors encoding EYFP and antisense-EYFP revealed for the first time that gene expression can be suppressed by co-expression of antisense RNA in Physarum. Quantitative analysis revealed that one copy of antisense expressing gene per EYFP gene was sufficient to completely suppress formation of the EYFP protein in Physarum.     

表达绿色荧光蛋白的重组耻垢分枝杆菌的构建

目的 建立可表达绿色荧光蛋白的耻垢分枝杆菌,便于对耻垢分枝杆菌进行直观检测和快速定量。方法利用PCR技术从真核表达质粒pLVTH扩增获得绿色荧光蛋白的编码基因,克隆人大肠埃希菌一分枝杆菌穿梭载体pMV261,建立重组质粒pMVGFP,并经酶切鉴定证实。利用电穿孔技术将pMVGFP转化入耻垢分枝杆菌,利用卡那霉素抗性筛选重组耻垢分枝杆菌克隆,扩大培养后直接涂片,荧光显微镜镜检。结果重组质粒pMVGFP构建正确;将重组耻垢分枝杆菌在荧光显微镜下观察,证实绿色荧光蛋白在重组耻垢分枝杆菌中的表达。结论自发释放荧光的重组耻垢分枝杆菌的成功建立,为研究结核病致病机制和快速筛选化学药物等奠定了基础。     

“Just add small molecules” cell-free protein synthesis: Combining DNA template and cell extract preparation into a single fermentation

Cell-free protein synthesis (CFPS) is a versatile biotechnology platform enabling a broad range of applications including clinical diagnostics, large-scale production of officinal therapeutics, small-scale on-demand production of personal magistral therapeutics, and exploratory research. The shelf stability and scalability of CFPS systems also have the potential to overcome cost and infrastructure challenges for distributing and using essential medical tests at home in both high- and low-income countries. However, CFPS systems are often more time-consuming and expensive to prepare than traditional in vivo systems, limiting their broader use. Much work has been done to lower CFPS costs by optimizing cell extract preparation, small molecule reagent recipes, and DNA template preparation. In order to further reduce reagent cost and preparation time, this work presents a CFPS system that does not require separately purified DNA template. Instead, a DNA plasmid encoding the recombinant protein is transformed into the cells used to make the extract, and the extract preparation process is modified to allow enough DNA to withstand homogenization-induced shearing. The finished extract contains sufficient levels of intact DNA plasmid for the CFPS system to operate. For a 10 mL scale CFPS system expressing recombinant sfGFP protein for a biosensor, this new system reduces reagent cost by more than half. This system is applied to a proof-of-concept glutamine sensor compatible with smartphone quantification to demonstrate its viability for further cost reduction and use in low-resource settings.     

Thymidine salvage in Pseudomonas stutzeri and Pseudomonas aeruginosa provided by heterologous expression of Escherichia coli thymidine kinase gene.

Unlike enteric bacteria, Pseudomonas spp. generally lack thymidine phosphorylase and thymidine kinase activities, thus preventing their utilization of exogenous thymine or thymidine and precluding specific radioactive labeling of their DNA in vivo. To overcome this limitation, a DNA fragment encoding thymidine kinase (EC 2.7.1.21) from Escherichia coli was cloned into pKT230, a small, broad-host-range plasmid derived from plasmid RSF1010. From transformed E. coli colonies, the recombinant plasmid bearing the thymidine kinase gene was conjugally transferred to Pseudomonas stutzeri, Pseudomonas aeruginosa, Pseudomonas mendocina, Pseudomonas alcaligenes, and Pseudomonas pseudoalcaligenes. Thymidine kinase activity was expressed in all of these species, and all gained the ability to incorporate exogenous [2-14C]thymidine into their DNA. Thymidine incorporation into P. stutzeri was enhanced 12-fold more in mutants lacking thymidylate synthetase activity. These mutants produced higher levels of thymidine kinase and were thymidine auxotrophs; thymineless death resulted from removal of thymidine from a growing culture.     

Efficient transfection of primary zebrafish fibroblasts by nucleofection

Although various gene delivery techniques are available, their application in zebrafish cell cultures has not been extensively studied. Here, we report that nucleofection of zebrafish primary embryonic fibroblasts results in higher transfection efficiency in comparison to other non-viral gene delivery methods. The transfection was performed using green fluorescent protein (GFP) gene constructs of a different size. Greatest DNA uptake was obtained with 4.9-kb plasmid, resulting in 43% GFP positive cells. Nucleofection with 7.4-kb pH2B-GFP plasmid followed by geneticin (G418) selection was successfully used to establish a cell line expressing nuclear histone 2B-GFP fusion protein. Efficient transfection of zebrafish fibroblasts by nucleofection offers a non-viral technique of plasmid delivery and can be used to overexpress genes of interest in these cells.     

Simultaneous detection and removal of organomercurial compounds by using the genetic expression system of an organomercury lyase from the transposon Tn<Emphasis Type="Italic">MERI1</Emphasis>

Using a newly identified organomercury lyase gene (merB3) expression system from Tn MERI1, the mercury resistance transposon first found in Gram-positive bacteria, a dual-purpose system to detect and remove organomercurial contamination was developed. A plasmid was constructed by fusing the promoterless luxAB genes as bioluminescence reporter genes downstream of the merB3 gene and its operator/promoter region. Another plasmid, encoding mer operon genes from merR1 to merA, was also constructed to generate an expression regulatory protein, MerR1, and a mercury reductase enzyme, MerA. These two plasmids were transformed into Escherichia coli cells to produce a biological system that can detect and remove environmental organomercury contamination. Organomercurial compounds, such as neurotoxic methylmercury at nanomolar levels, were detected using the biomonitoring system within a few minutes and were removed during the next few hours.     

The mitochondrial genome of the Basidiomycete fungus Pleurotus ostreatus (oyster mushroom)

In this study, the full mitochondrial genome of a basidiomycete fungus, Pleurotus ostreatus, was sequenced and analyzed. It is a circular DNA molecule of 73 242 bp and contains 44 known genes encoding 18 proteins and 26 RNA genes. The protein-coding genes include 14 common mitochondrial genes, one ribosomal small subunit protein 3 gene, one RNA polymerase gene and two DNA polymerase genes. In addition, one RNA and one DNA polymerase genes were identified in a mitochondrial plasmid. These two genes show relatively low similarities to their homologs in the mitochondrial genome but they are nearly identical to the known mitochondrial plasmid genes from another Pleurotus ostreatus strain. This suggests that the plasmid may mediate the horizontal gene transfer of the DNA and RNA polymerase genes into mitochondrial genome, and such a transfer may be an ancient event. Phylogenetic analysis based on the cox1 ORFs verified the traditional classification of Pleurotus ostreatus among fungi. However, the discordances were observed in the phylogenetic trees based on the six cox1 intronic ORFs of Pleurotus ostreatus and their homologs in other species, suggesting that these intronic ORFs are foreign DNA sequences obtained through HGT. In summary, this analysis provides valuable information towards the understanding of the evolution of fungal mtDNA.