Explore the vast range of titles available.

A set of mutated Encephalomyocarditis virus (EMCV) internal ribosome entry site (IRES) elements with varying strengths is generated by mutating the translation initiation codons of 10(th), 11(th), and 12(th) AUG to non-AUG triplets. They are able to control the relative expression of multiple genes over a wide range in mammalian cells in both transient and stable transfections. The relative strength of each IRES mutant remains similar in different mammalian cell lines and is not gene specific. The expressed proteins have correct molecular weights. Optimization of light chain over heavy chain expression by these IRES mutants enhances monoclonal antibody expression level and quality in stable transfections. Uses of this set of IRES mutants can be extended to other applications such as synthetic biology, investigating interactions between proteins and its complexes, cell engineering, multi-subunit protein production, gene therapy, and reprogramming of somatic cells into stem cells.

High expression level and long-term expression stability are required for therapeutic protein production in mammalian cells. Three commonly used promoters from the simian virus 40 (SV40), the CHO elongation factor 1α gene (EF1α), and the human cytomegalovirus major immediate early gene (CMV) and two matrix attachment regions from the chicken lysozyme gene (cMAR) and the human interferon β (iMAR) were evaluated for enhancing recombinant gene expression level and stability in stably transfected CHO cells. In the absence of MAR elements, the SV40 promoter gave lower expression level but higher stability than the EF1α promoter and the CMV promoter. The inclusion of MAR elements did not increase the integrated gene copies for all promoters but did enhance expression level for only the SV40 promoter. The enhanced gene expression was due to an increase in mRNA levels. Neither MAR elements enhance gene expression stability during long-term culture. The combinations of SV40 promoter and MAR elements are the best for obtaining both high expression level and stability. The information presented here would be valuable to those developing vectors for generation of CHO cell lines with stable and high productivity.

Promoters are essential on plasmid vectors to initiate transcription of the transgenes when generating therapeutic recombinant proteins expressing mammalian cell lines. High and sustained levels of gene expression are desired during therapeutic protein production while gene expression is useful for cell engineering. As many finely controlled promoters exhibit cell and product specificity, new promoters need to be identified, optimized and carefully evaluated before use. Suitable promoters can be identified using techniques ranging from simple molecular biology methods to modern high-throughput omics screenings. Promoter engineering is often required after identification to either obtain high and sustained expression or to provide a wider range of gene expression. This review discusses some of the available methods to identify and engineer promoters for therapeutic recombinant protein expression in mammalian cells.

Four versions of tricistronic vectors expressing IgG1 light chain (LC), IgG1 heavy chain (HC), and dihydrofolate reductase (DHFR) in one transcript were designed to compare internal ribosome entry site (IRES) and furin-2A (F2A) for their influence on monoclonal antibody (mAb) expression level and quality in CHO DG44 cells. LC and HC genes are arranged as either the first or the second cistron. When using mAb quantification methods based on the detection antibodies against HC Fc region, F2A-mediated tricistronic vectors appeared to express mAb at higher levels than the IRES-mediated tricistronic vectors in both transient and stable transfections. Further analysis revealed that more than 40% of products detected in stably transfected pools generated using the two F2A-mediated tricistronic vectors were aggregates. LC and HC from the F2A stably transfected pools were not properly processed, giving rise to LC+F2A+HC or HC+F2A+LC fusion proteins, LC and HC polypeptides with F2A remnants, and incorrectly cleaved signal peptides. Both IRES-mediated tricistronic vectors express mAb with correct sizes and signal peptide cleavage. Arrangement of LC as the first cistron in the IRES-mediated tricistronic vectors exhibits increased mAb expression level, better growth, and minimized product aggregation, while arrangement of HC as first cistron results in low expression, slower growth, and high aggregation. The results obtained will be beneficial for designing vectors that enhance mAb expression level and quality in mammalian cells.

Peat fuels representing four biomes of boreal (western Russia and Siberia), temperate (northern Alaska, USA), subtropical (northern and southern Florida, USA), and tropical (Borneo, Malaysia) regions were burned in a laboratory chamber to determine gas and particle emission factors (EFs). Tests with 25 % fuel moisture were conducted with predominant smoldering combustion conditions (average modified combustion efficiency (MCE) =0.82±0.08). Average fuel-based EFCO2 (carbon dioxide) are highest (1400 ± 38 g kg−1) and lowest (1073 ± 63 g kg−1) for the Alaskan and Russian peats, respectively. EFCO (carbon monoxide) and EFCH4 (methane) are ∼12 %–15 % and ∼0.3 %–0.9 % of EFCO2, in the range of 157–171 and 3–10 g kg−1, respectively. EFs for nitrogen species are at the same magnitude as EFCH4, with an average of 5.6 ± 4.8 and 4.7 ± 3.1 g kg−1 for EFNH3 (ammonia) and EFHCN (hydrogen cyanide); 1.9±1.1 g kg−1 for EFNOx (nitrogen oxides); and 2.4±1.4 and 2.0 ± 0.7 g kg−1 for EFNOy (total reactive nitrogen) and EFN2O (nitrous oxide). An oxidation flow reactor (OFR) was used to simulate atmospheric aging times of ∼2 and ∼7 d to compare fresh (upstream) and aged (downstream) emissions. Filter-based EFPM2.5 varied by > 4-fold (14–61 g kg−1) without appreciable changes between fresh and aged emissions. The majority of EFPM2.5 consists of EFOC (organic carbon), with EFOC ∕ EFPM2.5 ratios in the range of 52 %–98 % for fresh emissions and ∼14 %–23 % degradation after aging. Reductions of EFOC (∼7–9 g kg−1) after aging are most apparent for boreal peats, with the largest degradation in low-temperature OC1 that evolves at < 140  ∘C, indicating the loss of high-vapor-pressure semivolatile organic compounds upon aging. The highest EFLevoglucosan is found for Russian peat (∼16 g kg−1), with ∼35 %–50 % degradation after aging. EFs for water-soluble OC (EFWSOC) account for ∼20 %–62 % of fresh EFOC. The majority (> 95 %) of the total emitted carbon is in the gas phase, with 54 %–75 % CO2, followed by 8 %–30 % CO. Nitrogen in the measured species explains 24 %–52 % of the consumed fuel nitrogen, with an average of 35 ± 11 %, consistent with past studies that report ∼1/3 to 2∕3 of the fuel nitrogen measured in biomass smoke. The majority (> 99 %) of the total emitted nitrogen is in the gas phase, with an average of 16.7 % as NH3 and 9.5 % as HCN. N2O and NOy constituted 5.7 % and 2.9 % of consumed fuel nitrogen. EFs from this study can be used to refine current emission inventories.

We study the response of international investment flows to short- and long-run growth news. Among developed G7 countries, positive long-run news for domestic productivity induces a net outflow of investments, in contrast to the effects of short-run growth shocks. We document that a standard Backus, Keho, and Kydland (1994) (BKK) model fails to reproduce this novel empirical evidence. We augment this model with Epstein and Zin (1989) preferences (EZ-BKK) and characterize the resulting recursive risk-sharing scheme. The response of international capital flows in the EZ-BKK model is consistent with the data.

We investigate whether bank loan financing from 1994 to 2018 conveys valuable private information using a sample of over 10,000 bank loan announcements identified from 8-K filings. We show that the positive announcement effect is persistent and closely related to the information revealed in loan characteristics: The effect is stronger when deals have higher materiality, more favorable pricing, larger lead bank shares, and higher syndicate concentration. The effect is also stronger when lenders have higher credit quality and when credit market conditions are worse. The insignificant wealth effect documented in several early studies is potentially driven by small sample size.

The high contribution of secondary organic aerosol to the loading of fine particle pollution in China highlights the roles of volatile organic compound (VOC) oxidation. In this respect, particulate active metallic oxides in dust, like TiO2 and Fe ions, were proposed to influence the photochemical reactions of ambient VOCs. A case study was conducted at an urban site in Xi'an, northwest China, to investigate the origin and transformation of VOCs during a windblown dust-to-haze pollution episode, and the assumption that dust would enhance the oxidation of VOCs was verified. Local vehicle exhaust (25 %) and biomass burning (18 %) were found to be the two largest contributors to ambient VOCs. In the dust pollution period, a sharp decrease in the loading of VOCs and the aging of their components were observed. Simultaneously, the secondary oxygenated VOC fraction (i.e., methylglyoxal) increased. Source strength, physical dispersion, and regional transport were eliminated as major factors for the variation of ambient VOCs. In another aspect, about a 2- to 3-fold increase in the loading of iron (Fe) and titanium (Ti) was found in the airborne particles, together with a fast decrease in trans-/cis-2-butene ratios, which demonstrated that dust can accelerate the oxidation of ambient VOCs and the formation of secondary organic aerosol (SOA) precursors.

Urbanization is an issue that is strongly emerging in southern West Africa (sWA). There is a lack of full understanding on chemical compositions and personal exposure levels to fine particulate matter (hereafter defined as PE PM2.5) and its health risks related to various anthropogenic sources in this region. In this study, PE PM2.5 was studied in dry (January) and wet (July) seasons of 2016 for the first time to characterize the contributions of a domestic fire site (DF) to the exposure of women and a waste burning site (WB) to that of students in Abidjan, Côte d'Ivoire, and a motorcycle traffic site (MT) to that of drivers in Cotonou, Benin. The average PE PM2.5 mass concentrations were 331.7±190.7, 356.9±71.9 and 242.8±67.6 µg m−3 at DF, WB and MT sites for women, students and drivers, which were 2.4, 10.3 and 6.4 times the ambient PM2.5 concentrations, respectively. Elevated PE PM2.5 levels in the dry season were found at DF (358.8±100.5 µg m−3), WB (494.3±15.8 µg m−3) and MT (335.1±72.1 µg m−3) sites, on average 15 % higher than that at DF and 55 % higher at both WB and MT sites in the wet season. The seasonal variations were attributed to emission sources, meteorological factors and personal activities. In addition, the results show that geological material (35.8 %, 46.0 % and 42.4 %) and organic matter (34.1 %, 23.3 % and 24.9 %) were the major components of PE PM2.5 at DF, WB and MT sites. It is worth noting that the contribution of heavy metals was higher at WB (1.0 %) than at DF (0.7 %) and MT (0.4 %) sites, strongly influenced by waste burning emission. This results in the highest non-cancer risks of heavy metals to students, 5.1 and 4.8 times the values for women and drivers, respectively. By conducting organic speciation, fingerprints were used to access the exposure and identify the source contributions from typical local anthropogenic sources. The women's exposure concentration to particulate polycyclic aromatic hydrocarbons (PAHs) at DF (77.4±47.9 ng m−3) was 1.6 and 2.1 times, respectively, that of students at WB (49.9±30.7 ng m−3) and of drivers at MT (37.0±7.4 ng m−3). This can be associated with the higher contributions from solid fuels' burning and meat grilling activities to women, resulting in a level 5 times in exceedance of the cancer risk safety threshold (1×10-6). Phthalate esters (PAEs), commonly used as plasticizers in products, were in high levels in the student exposure PM2.5 samples (1380.4±335.2 ng m−3), owing to obvious waste burning activities nearby. The drivers' exposures to fossil fuel combustion markers of hopanes in PE PM2.5 at MT (50.9±7.9 ng m−3) was 3.0–3.3 times those for women at DF (17.1±6.4 ng m−3) and students at WB (15.6±6.1 ng m−3). Overall, the current study shows that wood combustion, waste burning, fugitive dust and motor vehicle emissions were the dominant sources of PE PM2.5 and mainly contributed to its toxicities. The exposure to the heavy metals Pb and Mn caused high non-cancer risks to students at WB, while the severe cancer risk of PAHs was found for women at DF via inhalation. The result of this study provides original data, initial perspective of PM2.5 personal exposure and health risk assessment in the developing areas. The information encourages the governments to improve the air quality and living standards of residents in this region.

The unique geographical location of the Tibetan Plateau (TP) plays an important role in regulating global climate change, but the impacts of the chemical components and atmospheric processing on the size distribution and mixing state of individual particles are rarely explored in the south-eastern margin of the TP, which is a transport channel for pollutants from Southeast Asia to the TP during the pre-monsoon season. Thus a single-particle aerosol mass spectrometer (SPAMS) was deployed to investigate how the local emissions of chemical composition interact with the transporting particles and assess the mixing state of different particle types and secondary formation in this study. The TP particles were classified into six distinct types, mainly including the largest fraction of the potassium-rich (K-rich) type in the total particles (30.9 %), followed by the biomass burning (BB) type (18.7 %). Most particle types were mainly transported from the sampling site's surroundings and along the Sino-Myanmar border, but the air mass trajectories from north-eastern India and Myanmar show a greater impact on the number fraction of the BB (31.7 %) and dust (18.2 %) types, respectively. Then, the two episodes with high particle concentrations showed that the differences in the meteorological conditions in the same trajectory clusters could cause significant changes in chemical components, especially the dust and aged elemental carbon (aged EC) types, which changed by a total of 93.6 % and 72.0 %, respectively. Ammonium and dust particles distribute at a relatively larger size (∼600 nm), but the size peak of other types is present at ∼440 nm. Compared with the abundant sulfate (97HSO4-), the low nitrate (62NO3-) internally mixed in TP particles is mainly due to the fact that nitrate is more volatilized during the transport process. The formation mechanism of secondary speciation demonstrates that the formation capacity of atmospheric oxidation is presumably affected by the convective transmission and the regional transport in the TP. However, the relative humidity (RH) could significantly promote the formation of secondary species, especially 97HSO4- and 18NH4+. This study provides new insights into the particle composition and size, mixing state, and ageing mechanism in high time resolution over the TP region.