Search

Reverse genetics is a useful tool for studying viruses and developing vaccines for coronaviruses. However, constructing and manipulating the coronavirus genome in Escherichia coli can be time-consuming and challenging due to its large size and instability. Homologous recombination, a genetic manipulation mechanism found in organisms, is essential for DNA repair, gene recombination, and genetic engineering. In yeast, particularly Saccharomyces cerevisiae, homologous recombination technology is commonly used for constructing gene expression plasmids and genome editing. In this study, we successfully split and spliced a 30 kb viral genome fragment using yeast homologous recombination. By optimizing the program parameters, such as homologous arm lengths and fragment-to-vector ratios, we achieved a splicing efficiency of up to 97.9%. The optimal parameters selected were a 60 bp homologous sequence size and a vector fragment ratio of 1:2:2:2:2:2 for yeast homologous recombination of large DNA fragments. [ABSTRACT FROM AUTHOR]

Late Permian to middle Triassic volcanic activities were very strong, however, volcanic records in the early Triassic strata are less reported than those of the Permo-Triassic boundary and the Triassic Olenekian-Anisian boundary in the Yangtze plate, especially within the Sichuan basin. We conduct zircon U-Pb dating and geochemical analysis of the tephra which was first found in the early Triassic Jialingjiang Formation from the Maliuping section, Hechuan, Chongqing. The volcanic ash in the paper yields the new 248.5 ± 0.7 Ma U-Pb age consistent with those of volcanic ashes in these contemporaneous strata in the Yangtze plate. Geochemical characters of whole-rock samples show lower contents in SiO2, K2O and higher components in Al2O3, CaO, MgO, relatively enriched LREE and depleted HREE with distinct negative Eu anomaly, and conspicuous Ba, Nb, Ta, Sr, P, Ti depletion and Th, U, K, Nd enrichment, which is similar to those of the Mung Bean rock of the Triassic Olenekian-Anisian boundary, and those of acidic volcanics from the Sanjiang orogenic belt and Shiwandashan-Qiangfang suture zone during the Early-Middle Triassic. Trace elements of whole rock and analysed zircons of the tuff imply its primary magma derived from Rhyodacite/Dacite and its tectonic setting of volcanic arc granite with continental crust affinity. The early Triassic volcanism during the syn-collision stage of the Paleo-Tethys evolution was less active than those of the Permo-Triassic boundary and the Triassic Olenekian-Anisian boundary, while the volcanic event may have a crucial effect on prolonging fully biotic recovery and entirely ecosystem turnover soon after the Permian-Triassic mass extinction. [ABSTRACT FROM AUTHOR]

Cap carbonate of the early Ediacaran period represents an abrupt climate shift from severe Marinoan glaciation to a post‐glacial warm environment. Some consensuses on the distinctive negative excursion of δ13Ccarb and the origin of its unique sedimentary structures have been reached over the past decades, but certain aspects such as the distribution and redox conditions of cap carbonate still remain controversial. To resolve these issues, we collected detailed samples of the Doushantuo cap carbonate from the Ganlong‐Fanyang section and the Poutoushang reservoir section in the Danzhai County, southeast Guizhou Province, respectively. We conducted carbon and oxygen isotope analysis and trace element analysis in this study. The Ganlong‐Fanyang section was possibly situated in a submarine highland because of its higher carbon isotope than that of the Potoushang section according to the carbon isotopic gradient. Negative carbon isotope excursions at the basal Doushantuo cap carbonate from the two sections correlate well with those from other equivalent cap carbonates and were corresponding to the first one (SN1 or EN1) of the carbon isotopic curve during the Ediacaran period, implying a remarkable global event after the post‐Marinoan glaciation. Geochemical features of trace elements and rare earth elements support an overall oxygen‐rich condition with syn‐depositional or pene‐contemporaneous hydrothermal activities and methane seeps during the deposition of cap carbonate. We reconstruct a new sedimentary model that the Doushantuo cap carbonates were mainly precipitated in relatively shallow‐ to deep‐water shelf environments without disturbance by abundant terrestrial materials, which may be on isolated platforms over the early developed grabens in a deep‐water basinal condition, rather than within the entire oceanic basin. [ABSTRACT FROM AUTHOR]

Urate oxidase (Uox) plays a pivotal role in uric acid (UA) degradation, and it has been applied in controlling serum UA level in clinical treatment of hyperuricemia (HUA). However, because Uox is a heterogenous protein to the human body, the immune rejections typically occur after intravenous administration, which greatly hampers the application of Uox-based agents. In this study, we used Lactococcus lactis NZ9000, a food-grade bacterium, as a host to express exogenous Uox genes, to generate the Uox-expressing engineered strains to treat HUA. Aspergillus flavus -derived Uox (aUox) and the "resurrected" human-derived Uox (hUox) were cloned into vector and expressed in NZ9000, to generate engineered strains, respectively. The engineered NZ9000 strains were confirmed to express Uox and showed UA-lowering activity in a time-dependent manner in vitro . Next, in an HUA mice model established by oral gavage of yeast paste, the UA levels were increased by 85.4% and 106.2% at day 7 and day 14. By contrast, in mice fed with NZ9000-aUox, the UA levels were increased by 39.5% and 48.3% while in mice fed with NZ9000-hUox were increased by 57.0% and 82.9%, suggesting a UA-lowering activity of both engineered strains. Furthermore, compared with allopurinol, the first-line agent for HUA treatment, mice fed with NZ9000-aUox exhibited comparable liver safety but better kidney safety than allopurinol, indicating that the use of engineered NZ9000 strains not only alleviated kidney injury caused by HUA, but could also avoided the risk of kidney injury elicited by using allopurinol. Collectively, our study offers an effective and safe therapeutic approach for HUA long-term treatment and controlling.