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911.
Citrate synthase is the initial enzyme in the tricarboxylic acid cycle of mitochondria. In plants and fungi, it is the second isozyme in the glyoxylate cycle of peroxisomes (or glyoxysomes), and it is also present in bacteria. Some of the biochemical reactions in the glyoxylate cycle of the ciliated protozoan Tetrahymena pyriformis depend upon mitochondrial enzymes, as T. pyriformis lacks some glyoxysome-specific enzymes. Here we demonstrate a new citrate synthase gene from Tetrahymena thermophila that is different from the mitochondrial counterpart. A potential peroxysome-targeted signal was detected in the N-terminus, suggesting the localization of the enzyme in peroxysomes. Phylogenetic analysis placed the Tetrahymena sequence in a clade consisting of a few sequences from eukaryotes such as cellular slime molds and two land plants, near a green sulfur bacterium and many proteobacteria as a sister group but not in a mitochondrial clade. Southern blot analysis revealed that this type of gene was absent from distantly related ciliates and other species of Tetrahymena except for the closest species, T. mallaccensis. The scattered presence of the bacterial-like genes among distantly related eukaryotes suggests three alternative interpretations of acquisition of the novel glyoxysomal citrate synthase gene via lateral gene transfer (LGT). (1) Some eukaryotes independently acquired the gene from a common bacterium or closely related bacteria via LGT. (2) A hypothetical eukaryote once acquired the gene, which was thereafter independently transferred from the eukaryote to other eukaryotes. (3) A single event of LGT (or duplication) occurred in a certain common ancestor of eukaryotes, followed by multiple losses in many eukaryotic lineages during the subsequent evolution. Considering the monophyly of the bacterial-like eukaryotic citrate synthase genes, the first model is somewhat unlikely, even though it is not impossible. The second and third models can rationally explain the present observation, so these models are discused in some detail. 相似文献
912.
Evidence for Multiple Lateral Transfers of the Circadian Clock Cluster in Filamentous Heterocystic Cyanobacteria Nostocaceae 总被引:1,自引:0,他引:1
Cyanobacteria are the first prokaryotes reported to show circadian rhythmicity, which is regulated by a cluster of three genes: kaiA, kaiB, and kaiC. Phylogenetic analysis of the kaiBC cluster in filamentous cyanobacteria of the family Nostocaceae including Nodularia spumigena and Nostoc linckia from Arubotaim Cave, Mt. Sedom, Israel, indicated that this cluster has experienced multiple lateral transfers. The transfers have occurred in different periods of the species evolution. The data obtained suggest that lateral transfers of the circadian clock cluster in filamentous cyanobacteria have been common and might have adaptive significance. 相似文献
913.
914.
A gregarious lifestyle affords the benefit of collective detectionof predators through the many-eyes effect. Studies of vigilanceare generally concerned with exploring the relationship betweenvigilance rates and group size. However, a mechanistic understandingof the rules individual animals use to achieve this group-levelbehavior is lacking. Building on a previous modeling approach,we suggest that individuals reconcile their own private informationagainst the social information they receive from their groupmates in order to decide whether to feed or be vigilant at anyone time. We present a novel modeling approach utilizing a Markovchain Monte Carlo process to describe the transition betweenvigilant and nonvigilant states. Many of our assumptions arebased qualitatively on recently published experimental observations.We vary the amount of social information and the fidelity withwhich individuals process this information and show that thishas a profound effect on the individual vigilance rate, theindividual vigilant bout length, and the proportion of vigilantindividuals at any one time. A wide range of group-level vigilancepatterns can be obtained by varying simple behavioral characteristicsof individual animals. We find that generally, increasing theamount of, and sensitivity to, social information generatesa more cooperative vigilance behavior. This model potentiallyprovides a theoretical and conceptual framework for examiningspecific real-life systems. We propose analyzing individual-baseddata from real animals by considering their group to be a connectednetwork of individuals, with information transfer between them. 相似文献
915.
Sebestyén MG Budker VG Budker T Subbotin VM Zhang G Monahan SD Lewis DL Wong SC Hagstrom JE Wolff JA 《The journal of gene medicine》2006,8(7):852-873
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. 相似文献
916.
917.
Human plasma phospholipid transfer protein (PLTP) contains six potential N-glycosylation sites (Asn-X-Ser). To study the role
of these sites on PLTP structure and function, seven variants in which asparagine (N) residues were converted to glycine (G)
were prepared by site-directed mutagenesis. These were N47G, N77G, N100G, N126G, N228G, N381G and N47, 77, 100, 126, 228, 381G (NnullG). These variants and wild-type (WT) PLTP were expressed in COS-7 cells. Intracellular and secreted PLTP mass was analyzed
by Western blots and quantitative enzyme-linked immunosorbent assay; PLTP activities in cellular lysates and media were based
on the transfer of [3H]dipalmitoylphosphatidylcholine from phospholipid single bilayer vesicles to HDL. NnullG was not detected intracellularly. N381G was similar to WT PLTP with respect to specific activity and secretion efficiency. The specific activities of N47G, N77G, N100G, N126G, N228G and N381G were similar in cell lysate (range = 67–90% WT) and medium (range = 65–77% WT). Intracellular masses of these PLTP variants
were similar to that of WT (Mean = 103% WT); mean secreted mass was 88% WT. These results suggest that secretion-competent
PLTP requires glycosylation but that no single glycosylation site is required. 相似文献
918.
小鼠-牛体细胞种间核移植 总被引:1,自引:0,他引:1
本文探讨了小鼠-牛异质胚构建的简便方法及小鼠体细胞核在牛卵母细胞中重新编程的可能性。以牛的卵母细胞为细胞质供体,用去除透明带及徒手切割的方法去核,设定电压1.5 KV/cm,脉冲时间40μsec,与小鼠皮肤成纤维细胞进行电融合的融合率为67.44%,卵裂率为30.23%。融合细胞经离子酶素-6-DMAP激活,用微滴内压制做窝的方法培养小鼠皮肤成纤维细胞异质胚,异质胚的最终发育阶段为8细胞期。结果表明,去透明带牛卵母细胞经切割法去核,可用于小鼠异质胚构建;微滴内做窝的体外培养方法可避免无透明带胚胎的聚合。 相似文献
919.
This article evaluates the procedures for determining the vial heat transfer coefficient and the extent of primary drying
through manometric temperature measurement (MTM). The vial heat transfer coefficients (Kv) were calculated from the MTM-determined temperature and resistance and compared with Kv values determined by a gravimetric method. The differences between the MTM vial heat transfer coefficients and the gravimetric
values are large at low shelf temperature but smaller when higher shelf temperatures were used. The differences also became
smaller at higher chamber pressure and smaller when higher resistance materials were being freeze-dried. In all cases, using
thermal shields greatly improved the accuracy of the MTM Kv measurement. With use of thermal shields, the thickness of the frozen layer calculated from MTM is in good agreement with
values obtained gravimetrically. The heat transfer coefficient “error” is largely a direct result of the error in the dry
layer resistance (ie, MTM-determined resistance is too low). This problem can be minimized if thermal shields are used for
freeze-drying. With suitable use of thermal shields, accurate Kv values are obtained by MTM; thus allowing accurate calculations of heat and mass flow rates. The extent of primary drying
can be monitored by real-time calculation of the amount of remaining ice using MTM data, thus providing a process analytical
tool that greatly improves the freeze-drying process design and control. 相似文献
920.
For the prediction of the air and product temperatures, the product moisture, and the air humidity during a coating process
in a Bohle Lab-Coater, a model was developed. The purpose of this work was to determine the limit moisture, the critical moisture,
and the constant for the exchange rate between both zones and to use these values for other sets of experiments to test the
model. The adaptation of the 3 parameters (limit moisture, critical moisture, and exchange rate constant), was done by calculation
of the product temperature in both zones for several sets of parameters in order to minimize the sum of square deviation between
the calculated and the measured product temperatures. This set of parameters was used to test the validity of the model. By
applying the model, the product temperature could be predicted based on the product, process, and equipment-related parameters.
Hence, the model can be used to theoretically investigate the influence of different process paramaters. The mean difference
between the predicted, and measured product temperatures in the steady state is ≈2 up to 3 K using the determined parameter
set for the limit moisture, the critical moisture, and the exchange rate constant. The model is useful for the prediction
of the air and product temperatures, the product moisture, and air humidity during a coating process in the Bohle Lab-Coater
using round, biconvex tablets. 相似文献