The transformation of the spatial structure of a Dictyostelium discoideum population in response to environmental changes induced by this population was investigated. A comparative analysis of the spatial and temporal characteristics of the D. discoideum colony is given for two cases: (a) when the colony is cultivated on a bacterial lawn, i.e. under conditions close to natural, and (b) in the absence of the bacterial lawn when the colony grows on the nutrient substrate enriched with folic acid. It is shown that the environmental changes induced by cell metabolism modify the spatial structure of the D. discoideum population first, the rate of population propagation falls drastically, which correlates with a decrease in the substrate pH; second, the spatial redistribution of the D. discoideum cell density correlates with the redistribution of folic acid in the substrate. The mechanism of the environment impact on the D. discoideum colony transformation is discussed.

Agar↗

PubMedDate not supplied

[Quantitative analysis of variability of electrocardiograms typical for polymorphic arrhythmias].

A new approach to the analysis of variability of electrocardiograms (ECGs) typical of polymorphic arrhythmias is developed. In these ECGs, separate QRS complexes can be often hardly identified. As a result, the mathematical methods that have been elaborated hitherto are not suitable for such arrhythmias. The approach presented here is based on the quantitative estimation of the variability of neighboring parts of the ECG. In this case, the necessity of the identification of separate QRS complexes ceases to be significant. Based on this approach, the analysis of normalized ECG variability is developed in the framework of which two indices that characterize the oscillation variability and its changes in time are related to a part of the ECG and/or the ECG as a whole. Variations of these indices allow both the polymorphism of a separate ECG to be estimated and different ECGs to be compared with each other. The method presented may be useful in studies of the mechanisms and in the diagnosis of polymorphic arrhythmias.

Arrhythmias, Cardiac↗

PubMedDate not supplied

[Distribution and functional significance of A/T tracts in promotor sequences of Escherichia coli].

Distribution of the A/T tracts described in earlier publications in the region extending from nucleotide -250 to +150 relative to the transcription initiation site of gene transcribed regions adjacent to promoter was studied. Upstream of the -35 region a succession of A/T tracts was discovered distributed at a shorter distance one from another than in analogous elements of the transcribed region (1 and 1.5 helix turns, respectively). Such a positional dependence suggests different functional manifestation of A/T tracts at different transcription steps. Single initiation using the T7D promoter mutant derivatives devoid of A/T tracts in two critical positions, +41 and , yielded shortened products of the corresponding length. One might speculate that such elements adjacent to promoter region play a significant role in transcription complex functioning.

AT Rich Sequence↗

PubMedDate not supplied

[Levels in the structural organization of Escherichia coli promoter DNA].

A number of additional structural elements were identified by statistic analysis of nucleotide sequences in promoters recognized by Escherichia coli RNA polymerase. Together with canonical hexanucleotides, these elements characterize different levels in the structural organization of promoter DNA. Sequence motifs exhibiting the highest statistical significance, which dominate in the contact regions with RNA polymerase alpha and sigma subunits, are considered as targets for specific interaction with RNA polymerase. A typical feature of these elements is the presence of easily deformable dinucleotides (TG, CA and TA) or tracts containing only A/T base pairs. Thus, we noticed that the frequency of occurrence of TA in the promoter DNA is essentially higher than the average value for the genome. Besides the regions of specific interaction with RNA polymerase, these dinucleotides are often located in the number of other sites periodically distributed along the promoter DNA. This preferred disposition suggests that deformable elements participate in the adaptive conformational transitions of the promoter DNA favoring optimal configuration of the transcription complex. Probably, the most important feature of promoter DNA revealed by statistic analysis is the presence of A/T-tracts regularly distributed in the wide range from -160 up to +75 relative to the transcription start point. Both of these spatially distributed elements (TA dinucleotides and A/T-tracts) are linked with canonical regions and, therefore, may contribute to the conformational or dynamic features of the transcription machinery. Having high statistic significance, these elements might be considered as additional factors discriminating the promoter DNA on the background of other nucleotide sequences in the genome.

Base Sequence↗

PubMedDate not supplied

[Three-dimensional reconstruction of synapse and dendritic spines in the hippocampus of rats and ground squirrels: new paradigms of the structure and function of a synapse].

The article reviews the literature data and results obtained by the authors concerning synaptic plasticity and remodeling of synaptic organelles in the central nervous system. Modern techniques of laser scanning confocal microscopy and serial thin sectioning for in vivo and in vitro studies of dendritic spines including a correlation between morphological changes and synaptic transmission efficiency are discussed, particularly, in relation to long-term potentiation. Organization of different types of dendritic spines and involvement of filopodia in spine genesis are examined. Significance of serial ultrathin sections for unbiased quantitative stereological analysis and three-dimensional reconstructions is discussed. The contact of one dendritic spine with two presynaptic boutons (multiple synapses) on both CA1 mushroom dendritic spines is discussed. The analyzed findings suggest new ideas for organization and functioning of synapses.

Animals↗

PubMedDate not supplied

[Specificiety of DNA-protein interactions within transcription complexes of Escherichia coli].

Current requirement for description of each new promoter assumes identification of all DNA-protein and protein-protein contacts important for transcription complex formation. Experimental approaches allow estimating which one of seven alternative sigma-subunits is employed for RNA synthesis and verifying transcription dependence on known regulatory proteins. Promoter sequence by itself also contains this information. That is why, the type of promoter as well as potential regulatory proteins with high probability may be proposed, if the transcription start point has been determined. Transcription activity of the promoter is usually less predictive. It depends on the specific contacts formed by sigma-subunits with correspondent conservative elements and on many other non-specific factors that are hardly taken into account. Interaction with RNA polymerase alpha-subunits seems does not require any particular functional group of nucleotides thus exemplifying non-sequence-specific binding within binary polymerase-promoter complexes. The role of this interaction in the transcription complex formation is the main subject of this survey that summarizes our own experimental results and the data of other authors. Attempts have been made to compare nucleotide sequences of the promoters recognized by different sigma-factors within putative contact regions with alpha-subunits and to discuss regulatory propensity of free alpha-subunits.

Base Sequence↗

PubMedDate not supplied

[Do external or internal reasons determine the synchronicity of cell division at early stages of embryogenesis?].

By the method of computer simulation the 2-dimensional diagram, which reveals the dependence of the degree of cell division synchronization on genetic variation and environment variety, was obtained. The diagram demonstrates many trajectories of the cell system self-organization. It was shown that synchronization on the early stages of loach spawn embryogenesis may be obtained by the combination of various internal and external factors.

Cell Division↗

PubMedDate not supplied

[Specific modification of the alpha-subunit of Escherichia coli Rna polymerase by monomercuric derivative of fluorescein mercuric acetate].

The method for specific modification of Escherichia coli RNA polymerase by a monomercuric derivative of fluorescein--fluoresceinmonomercuracetate (FMMA)--a specific reagent for SH-groups of proteins is suggested. It is shown, that in conditions of equimolar FMMA/enzyme ratio the fluorescent label interacts preferantially with a single sulfhydryl group in alpha-subunit of RNA polymerase. The mercaptide bonding formation is followed by significant alterations of all spectral parameters of FMMA, but has no effect on the kinetic parameters (KB and k2) of RNA synthesis initiation nor does it lead to inhibition of the total RNA synthesis. The modification presented may be used in structural and topological investigations of RNA polymerase functioning.

Binding Sites↗

PubMedDate not supplied

[Spectral analysis of nucleotide sequences].

The data of Fourier-analysis of nucleotide sequences are discussed. The existence of reflexes corresponding to regular position of nucleotides (mainly T and G) with 3-base period is the most striking feature of both phage and viral nucleic acid sequences spectra. The amplitude and phase of the similar reflexes in the dinucleotide spectra obtained by digital computing of Fourier-transform, give specific information on amino acid composition, codon bias, amino acid relations. The width of frequency band characterizes a tendency to nucleotide clustering or to separate existence. The blurring of reflexes shows the disturbance of far order in the regular nucleotide "lattice". The two-dimensional spectral analysis supports the existence of far correlation in nucleotide positions.

Base Sequence↗

PubMedDate not supplied

[Structural changes in proteins of the bacteriophage T4 basal plate resulting from the attachment of long fibrils].

The effect of the attachment of long tail fibers on the structure of proteins of the bacteriophage T4 baseplate was studied by digital processing of electron microscopic images. The attachment of the long fibers was found to result in dramatical changes of the proteins of the baseplate plag, while the wedges, to which the long fibers are attached, undergo only slight changes. We studied the baseplates with one to six attached fibers and found that the attachment of one fiber resulted in the change of the entire baseplate, although the wedge located in the vicinity of the fiber attachment changed to a greater extent. Only after the attachment of three and more fibers the changes of the same kind occurred through the entire baseplate.

Microscopy, Electron↗

PubMedDate not supplied

[Model of reversible phage interaction with cell receptors].

A model of the bacteriophage behavior at the reversible adsorption stage was investigated. The ratio of concentration of long fibres bound with receptors on bacterial surface to the total concentration of the fibres was taken to be efficiency range of reversible adsorption. To determine this value the expressions for concentrations of all the intermediate forms of the long fibres binding were obtained. The relationship between reversible adsorption efficiency and concentrations of receptors with various values of corresponding constants was computed. The conditions providing different types of cooperativeness in the behavior of the baseplate elements in the process of reversible adsorption were analysed.

Bacteriophages↗

PubMedDate not supplied

[Does taxis exist in bacterial viruses?].

By way of example of interaction of T4 bacteriophage with E. coli bacterium the scenario of enhancement of sorption of phages on bacteria through the remote mechanism of their cyclic interaction has been considered. An enlargement of the typical phage size, when its fibrillae are opened, underlies this mechanism. Modification of the structure of phages also occurs through the medium by release of products of bacterial metabolism into it. Allied questions related to investigation of physicochemical and biological processes, which require to take into account "fluffing" of microparticles. The medium-induced change of volume of microparticles leads to spatial cooperative effects with non-linear dynamics. Such phenomena are possible in all diffusional processes in biology, chemistry and physics.

Bacteriophage T4↗

PubMedDate not supplied

[From disorder to order using the example of the function of phage T4 baseplate].

The structure of key elements of T4 baseplate distal part was investigated by electron microscopy and image processing. The functional aspects of interaction of distal part structures in cell infection process were discussed. According to the results obtained earlier the baseplate functioning was suggested to be like a synchronization process of the complex protein structure caused by variation of external factors.

Microscopy, Electron↗