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排序方式: 共有112条查询结果,搜索用时 15 毫秒
1.
Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state 总被引:6,自引:1,他引:5
The genes for cellobiose utilization are normally cryptic in Escherichia
coli. The cellobiose system was used as a model to understand the process
by which silent genes are maintained in microbial populations. Previously
reported was (1) the isolation of a mutant strain that expresses the
cellobiose-utilization (Cel) genes and (2) that expression of those genes
allows utilization of three beta- glucoside sugars: cellobiose, arbutin,
and salicin. The Cel gene cluster has now been cloned from that mutant
strain. In the course of locating the Cel genes within the cloned DNA
segment, it was discovered that inactivation of the Cel-encoded hydrolase
rendered the host strain sensitive to all three beta-glucosides as potent
inhibitors. This sensitivity arises from the accumulation of the
phosphorylated beta- glucosides. Because even the fully active genes
conferred some degree of beta-glucoside sensitivity, the effects of
cellobiose on a series of five Cel+ mutants of independent origin were
investigated. Although each of those strains utilizes cellobiose as a sole
carbon and energy source, cellobiose also acts as a potent inhibitor that
reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand,
wild-type strains that cannot utilize cellobiose are not inhibited. The
observation that the same compound can serve either as a nutrient or as an
inhibitor suggests that, under most conditions in which cellobiose will be
present together with other resources, there is a strong selective
advantage to having the cryptic (Cel0) allele. In those environments in
which cellobiose is the sole, or the best, resource, mutants that express
the genes (Cel+) will have a strong selective advantage. It is suggested
that temporal alternation between these two conditions is a major factor in
the maintenance of these genes in E. coli populations. This alternation of
environments and fitnesses was predicted by the model for cryptic-gene
maintenance that was previously published.
相似文献
2.
Selection-induced mutations are nonrandom mutations that occur as specific
and direct responses to environmental challenge. Examples of
selection-induced mutations have been reported both in bacteria and in
yeast. I previously showed (Hall 1988) that excisions of the mobile genetic
element IS150 from within bglF are selection induced and argued that they
occurred because they were potentially advantageous under the selective
conditions employed. Mittler and Lenski (Mittler and Lenski 1992) have
argued that such excisions are not selection induced but that they occur
randomly in nondividing cells. Here I provide further evidence that IS150
excisions are induced by selection and that the excisions are immediately,
rather than only potentially, advantageous to the cell. I also provide
evidence that excisions, which Mittler and Lenski claim occur randomly in
saturated broth cultures, actually occur after samples from those cultures
are plated onto selective medium.
相似文献
3.
Alexei N. Nekrasov Alexei A. Zinchenko 《Journal of biomolecular structure & dynamics》2013,31(5):553-561
Abstract The novel method allowing identification of protein structure elements responsible for catalytic activity manifestation is proposed. Structural organization of various hydrolases was studied using the ANIS (ANalysis of Informational Structure) method. ANIS allows to reveal a hierarchy of the ELements of Information Structure (ELIS) using protein amino acid sequence. The ELIS corresponds to the variable length sites with an increased density of structural information. The amino acid residues forming the enzyme catalytic site were shown to belong to the different top-ranking ELIS located in the contact area of the corresponding spatial structure clusters. In the protein spatial structure catalytic sites are located in the area of contact between fragments of polypeptide chain (structural blocs) allocation to the different top-ranking ELIS. According to our results we concluded that structural blocks corresponding to top-ranking ELIS are crucial for protein functioning. Such regions are structurally independent, and their determinate mobility relative to each other is vital for an efficient enzymatic reaction to occur. 相似文献
4.
Nekrasov AN 《Journal of biomolecular structure & dynamics》2002,20(1):87-92
Several classifications of protein spatial structures and their structural elements are known. This makes revealing of the relation between these structural elements and sequence fragments rather topical. The most important move in this direction would be the determination of positional sensitivity levels and ranges between the residues in protein sequences. In this work the Shannon-Weaver informational entropy was used as a disorder criterion for solving this problem. This entropy was computed as function of the distance between the amino acid residues in different sets of unhomological protein sequences. Similarity of this function for different sets of protein sequences was shown. Analysis of informational entropy allows detecting a long-range positional correlation (> or =30) between the amino acid residues and oscillations with periods of 3.6 and 2.9. These oscillation periods correspond to periodicity of alpha- and 3(10)-helices. 相似文献
5.
Surovtsev IV Razumov IA Nekrasov VM Shvalov AN Soini JT Maltsev VP Petrov AK Loktev VB Chernyshev AV 《Journal of theoretical biology》2000,206(3):407-417
A statistical approach is presented to model the kinetics of cell distribution in the process of ligand-receptor binding on cell surfaces. The approach takes into account the variation of the amount of receptors on cells assuming the homogeneity of monovalent binding sites and ligand molecules. The analytical expressions for the kinetics of cell distribution have been derived in the reaction-limited approximation. In order to demonstrate the applicability of the mathematical model, the kinetics of binding the rabbit, anti-mouse IgG with Ig-receptors of the murine hybridoma cells has been measured. Anti-mouse IgG was labeled with fluorescein isothiocyanate (FITC). The kinetics of cell distribution on ligand-receptor complexes was observed during the reaction process by real-time measuring of the fluorescence and light-scattering traces of individual cells with the scanning flow cytometer. The experimental data were fitted by the mathematical model in order to obtain the binding rate constant and the initial cell distribution on the amount of receptors. 相似文献
6.
High-level expression of the Endo-beta-N-acetylglucosaminidase F2 gene in E.coli: one step purification to homogeneity 总被引:1,自引:0,他引:1
The Endo F2gene was overexpressed in E.coli as a fusion protein joined to
the maltose-binding protein. MBP-Endo F2was found in a highly enriched
state as insoluble, inactive inclusion bodies. Extraction of the inclusion
bodies with 20% acetic acid followed by exhaustive dialysis rendered the
fusion protein active and soluble. MBP-Endo F2was digested with Factor
Xaand purified on Q-Sepharose. The enzyme was homogeneous by SDS-PAGE, and
appeared as a single symmetrical peak on HPLC. Analysis of the
amino-terminus demonstrated conclusively that recombinant Endo F2was
homogeneous and identical to the native enzyme.
相似文献
7.
L. N. Shingarova L. E. Petrovskaya A. N. Nekrasov E. A. Kryukova E. F. Boldyreva S. A. Yakimov S. V. Guryanova D. A. Dolgih M. P. Kirpichnikov 《Russian Journal of Bioorganic Chemistry》2010,36(3):301-309
The tumor necrosis factor (TNF) is a proinflammatory cytokine that plays a pivotal role in the regulation of the human immune system. Studies of the TNF functional topography are a challenging task in bioengineering. We have produced genes encoding the peptides D1 (3–30), D2 (31–85), D3 (86–114), and D4 (115–157), which correspond to isolated fragments of the informational structure of TNF. These genes were expressed in E. coli cells at a high level in a soluble form. We have shown that hybrid proteins SD2 and SD4 tend to form high-molecular aggregates, which can be destroyed by urea treatment. Purified peptides D1, D3, and D4 possess a similar secondary structure with dominating beta-structural elements. The analysis of the biological activity of these peptides has shown that they do not exhibit cytotoxic properties on L929 murine fibroblasts. The simultaneous addition of D1 with full-length TNF results in the concentration dependent suppression of TNF activity. 相似文献
8.
9.
10.
Svirshchevskaya E Alekseeva L Marchenko A Benevolenskii S Berzhec VM Nekrasov A 《Journal of bioinformatics and computational biology》2006,4(2):389-402
Sub-unit vaccines are synthetic or recombinant peptides representing T- or B-cell epitopes of major protein antigens from a particular pathogen. Epitope selection requires the synthesis of peptides that overlap the protein sequences and screening for the most effective ones. In this study a new method of immunogenic peptide selection based on the analysis of information structure of protein sequences is suggested. The analysis of known B-cell epitope location in the information structure of Aspergillus fumigatus proteins Asp f 2 and Asp f 3 has shown that epitopes are scattered along the sequences of proteins for the exception of sites with Increased Degree Information Coordination (IDIC). Based on these results peptides from different allergens such as Asp f 2, Der p 1, and Fel d 1 were selected and produced in a recombinant form in the context of yeast virus-like particles (VLPs). Immunization of mice with VLPs containing peptides form allergens has induced the production of IgG able to recognize full-length antigens. This result suggests that the analysis of information structure of proteins can be used for the selection of peptides possessing cryptic B-cell epitope activity. 相似文献