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981.
An intracellular esterase from the yeast Kluyveromyces marxianus CBS 1553 with interesting enantioselective hydrolytic activity towards racemic esters of 1,2-O-isopropylidene glycerol (IPG) was purified and characterized. Optimal culture conditions for the obtainment of the enantioselective esterase on a 5 l-fermentation scale were investigated. Two esterase activities (EST1 and EST2) in the crude cell extract were identified by native PAGE with specific activity staining and separated from each other by anion-exchange chromatography. EST1 showed higher activity and enantioselectivity than EST2 in the resolution of racemic IPG acetate and was further purified by hydrophobic interaction chromatography and preparative electrophoresis (final specific activity approximately = 300 U mg(-1), showing a main protein band with a molecular mass of 29 kDa. EST1 showed optimal activity between pH 8.0 and 10.0 and was stable in the pH range 7.0-10.0. Moreover, it was rather thermostable and active up to 80 degrees C, and retained most of its activity in the presence of 15% (v/v) of various organic solvents. The enzyme showed similar Vmax in the hydrolysis of the acetate esters of IPG, whereas the Km value towards (S)-IPG acetate was significantly lower than the one towards the (R)-enantiomer (5.3 and 70 microM, respectively). Finally, comparison of EST1 activity in the presence of different glycerol esters and synthetic substrates with different chain lengths showed a strong preference of this biocatalyst for short-chain substrates. 相似文献
982.
Mela F Fritsche K Boersma H van Elsas JD Bartels D Meyer F de Boer W van Veen JA Leveau JH 《FEMS microbiology ecology》2008,66(1):45-62
Plasmid pTer331 from the bacterium Collimonas fungivorans Ter331 is a new member of the pIPO2/pSB102 family of environmental plasmids. The 40 457-bp sequence of pTer331 codes for 44 putative ORFs, most of which represent genes involved in replication, partitioning and transfer of the plasmid. We confirmed that pTer331 is stably maintained in its native host. Deletion analysis identified a mini-replicon capable of replicating autonomously in Escherichia coli and Pseudomonas putida. Furthermore, plasmid pTer331 was able to mobilize and retromobilize IncQ plasmid pSM1890 at typical rates of 10(-4) and 10(-8), respectively. Analysis of the 91% DNA sequence identity between pTer331 and pIPO2 revealed functional conservation of coding sequences, the deletion of DNA fragments flanked by short direct repeats (DR), and sequence preservation of long DRs. In addition, we experimentally established that pTer331 has no obvious contribution in several of the phenotypes that are characteristic of its host C. fungivorans Ter331, including the ability to efficiently colonize plant roots. Based on our findings, we hypothesize that cryptic plasmids such as pTer331 and pIPO2 might not confer an individual advantage to bacteria, but, due to their broad-host-range and ability to retromobilize, benefit bacterial populations by accelerating the intracommunal dissemination of the mobile gene pool. 相似文献
983.
A thixotropic hydrogel from chemically cross-linked guar gum: synthesis, characterization and rheological behaviour 总被引:1,自引:0,他引:1
Polysaccharide guar gum (GG) was cross-linked in an alkaline solution with polyethylene glycol diglycidyl ether (PEGDGE) to create a new hydrogel. The GG hydrogel was examined by FT-IR spectroscopy, AFM analysis and SEM analysis. The water uptake of the GG hydrogel was measured at different pHs, and rheological studies were performed to verify the thixotropic nature of the material. Rheological studies revealed the pseudoplastic behaviour of the GG hydrogel and its thixotropic nature. AFM analysis on a sample which was subjected to shear stress showed the presence of nanoparticles in the hydrogel. When the sample was left to settle, the gel surface returned to its original homogenous morphology. The thixotropic and injectable nature of the GG hydrogel suggest its possible use in biomedical applications. 相似文献
984.
The radial arrangement of the human chromosome 7 in the lymphocyte cell nucleus is associated with chromosomal band gene density 总被引:1,自引:1,他引:0
In the nuclei of human lymphocytes, chromosome territories are distributed according to the average gene density of each chromosome. However, chromosomes are very heterogeneous in size and base composition, and can contain both very gene-dense and very gene-poor regions. Thus, a precise analysis of chromosome organisation in the nuclei should consider also the distribution of DNA belonging to the chromosomal bands in each chromosome. To improve our understanding of the chromatin organisation, we localised chromosome 7 DNA regions, endowed with different gene densities, in the nuclei of human lymphocytes. Our results showed that this chromosome in cell nuclei is arranged radially with the gene-dense/GC-richest regions exposed towards the nuclear interior and the gene-poorest/GC-poorest ones located at the nuclear periphery. Moreover, we found that chromatin fibres from the 7p22.3 and the 7q22.1 bands are not confined to the territory of the bulk of this chromosome, protruding towards the inner part of the nucleus. Overall, our work demonstrates the radial arrangement of the territory of chromosome 7 in the lymphocyte nucleus and confirms that human genes occupy specific radial positions, presumably to enhance intra- and inter-chromosomal interaction among loci displaying a similar expression pattern, and/or similar replication timing. 相似文献
985.
Gast D Riedle S Kiefel H Müerköster SS Schäfer H Schäfer MK Altevogt P 《Experimental cell research》2008,314(13):2411-2418
L1 cell adhesion molecule (L1-CAM) is a transmembrane cell adhesion molecule initially defined as a promigratory molecule in the developing nervous system. L1 is also overexpressed in a variety of human carcinomas and is associated with bad prognosis. In carcinoma cell lines L1 augments cell motility and metastasis, tumor growth in nude mice and induces expression of L1-dependent genes. It is not known whether L1-signaling requires ligand binding. The RGD motif in the sixth Ig domain of L1 is a binding site for integrins. In the present study we analyzed the role of RGDs in L1-signaling using site-directed mutagenesis combined with antibody blocking studies. We observed that L1-RGE expressing HEK293 cells showed reduced cell–cell binding, cell motility, invasiveness and tumor growth in NOD/SCID mice. The RGE-mutation impaired L1-dependent gene regulation and antibodies to αvβ5 integrin had similar effects. Mutant L1 was unable to translocate to the nucleus. Our findings highlight the importance of the RGD site in L1 for human tumors and suggest that nuclear signaling of L1 is dependent on integrins. 相似文献
986.
987.
Identification and characterization of an essential telomeric repeat binding factor in fission yeast 总被引:1,自引:0,他引:1
Whereas mammalian cells harbor two double strand telomeric repeat binding factors, TRF1 and TRF2, the fission yeast Schizosaccharomyces pombe has been thought to harbor solely the TRF1/TRF2 ortholog Taz1p to perform comparable functions. Here we report the identification of telomeric repeat binding factor 1 (Tbf1), a second TRF1/TRF2 ortholog in S. pombe. Like the Taz1p, the identified Tbf1p shares amino acid sequence similarity, as well as structural and functional characteristics, with the mammalian TRF1 and TRF2 proteins. This family of proteins shares a common architecture with two separate structural domains. An N-terminal domain is necessary and sufficient for the formation of homodimers, and a C-terminal MYB/homeodomain mediates sequence specific recognition of double-stranded telomeric DNA. The identified Tbf1p binds S. pombe telomeric DNA with high sequence specificity in vitro. Targeted deletion of the tbf1 gene reveals that it is essential for survival, and overexpression of the tbf1 gene leads to telomere elongation in vivo, which is dependent upon the MYB domain. These data suggest that fission yeast, like mammals, have two factors that bind double-stranded telomeric DNA and perform distinct roles in telomere length regulation. 相似文献
988.
989.
Nervous system tumors are one of the leading causes of cancer related death. Specific mechanisms facilitating the invasive
behavior of gliomas remain obscure. Advanced simulation models of the in vivo response to therapy conditions should potentially
improve malignant glioma treatment. Expressional profiling of vimentin––one of reliable pro-invasive tumor makers––in those
simulation models was the goal of this study, in order to estimate a pro-invasive response of surviving malignant glioma cells
under clinically relevant therapeutic conditions. Human U87-MG malignant glioma cells were used. These cells are characterized
by the wild p53-phenotype, which is relevant for the majority of primary malignant glioblastomas. Experimental design foresaw the cells to
undergo either irradiation or chemo-treatment with temozolomide alone, or combined treatment. Expression profiling of vimentin
was performed by quantitative “Real-Time”-PCR under all treatment conditions simulating diverse tumor regions. Here we demonstrated
that vimentin expression patterns in human malignant glioma cells strongly depend on cellular density, algorithms of drug
delivery and chemo/radio treatment. Substantial differences were recognized between immediate and late therapy effects. Significant
increase in vimentin expression levels was detected particularly in low-density cell cultures under durable treatment with
constant concentration levels of temezolomide. Simulation of variable intratumoral regional conditions (central intratumoral
regions vs. disseminated malignant cells in peripheral regions) demonstrated differential response of vimentin expression
in malignant glioma cell cultures treated under clinically relevant conditions. Slight ebbing of expression levels as late
effects of the treatment in confluent cultures may correspond to necrotic processes clinically observed in central intratumoral
regions. Contrary, in disseminated malignant cells of peripheral regions therapy resulted in vimentin-inducing effects. This
is in agreement with the clinical observations of an increased aggressiveness and malignancy grade of post-operatively chemo/radio-treated
malignant gliomas. 相似文献
990.