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T I Smirnova

Publications and source records attributed to T I Smirnova.

16 recordsLinked to original sources
PubMed2001

[Detection of concealed "illegitimate" nuclei in tetrad analysis of the diploid progeny of heterokaryons in Saccharomyces cerevisiae].

In this work, the studies on the previously detected phenomenon of concealed heterokaryosis in Saccharomyces cerevisiae were continued. In genetic and Southern blotting experiments, one of the nuclei in the heterokaryon was shown to be active (capable of division and ensuring the corresponding cell phenotype), whereas the other was not expressed until the heterokaryotic clone was transferred to the medium selective for this concealed nucleus. Moreover, the concealed nucleus was able to assume the active state after fusion with the second parental nucleus. It was analyzed whether the nuclei with new marker combinations occurring in meiosis can behave as exceptional nuclei. Tetrad analysis of hybrids carrying the kar1 mutation in their nuclei revealed the relatively high percentage of exceptional tetrads (more than 10%). One spore in these tetrads usually formed diploid cells capable of sporulation. The presented data of genetic and molecular biological studies testify in favor of the assumption that abnormal spores contain two nuclei, which form an "illegitimate" hybrid after fusion. An extraneous spore (termed x) has usually a genotype close to that of one of the spores in this tetrad. Thus, it was assumed that the additional DNA replication round occurs in the absence of cell division during one of meiotic divisions. Results of cytological analysis conducted by the method of specific DNA staining confirmed the existence of exceptional tetrads, one spore of which contains two nuclei.

Cell Nucleus↗
PubMed2000

[Cryptic heterokaryons in strains of Saccharomyces cerevisiae. Conditions for detecting a cryptic nucleus].

A phenomenon discovered earlier, cryptic heterokaryosis in Saccharomyces yeast, has been further investigated. A phenotypically silent nucleus in a yeast cell may resume its expression after fusion with another parental cell. The resulting hybrid is capable of sporulation. By the growth of a cytoductant with an expressing nucleus from one parent and a silent nucleus from the other parent on suitable selective media, the silent nucleus can be activated. The presence of deletion or insertion mutations in several genes in YPH strains allows nuclei of the YPH type to be traced not only genetically but also by blotting.

Cell Nucleus↗
PubMed1999

Interaction of Gd(III) MRI contrast agents with membranes: a review of recent EPR studies.

Rational development of new selective paramagnetic contrast agents (PCAs) requires a detailed understanding of their interactions with biological macromolecules. This report shows how some of these interactions can be studied with electron paramagnetic resonance (EPR) through examples of Gd3+ complexes interactions with model phospholipid membranes. It is shown that the spin label EPR method can be used to detect: (i) presence and possible location of lipophilic contrast agents in the model membranes, (ii) changes and distortions in membrane organization upon interaction with the PCAs, and (iii) changes in the local polarity of the bilayer and its phase behavior due to addition of Gd3+ complexes. This work demonstrates that interaction of Gd3+ complexes with phospholipid bilayers can be observed directly from changes in their continuous wave (CW) EPR spectra obtained at frequencies higher than X-band (9.5 GHz), where signals arising from aqueous and lipid-bound Gd3+ complexes become resolved. Analysis of frequency dependence of the effective g-factors of the EPR signal provides estimates of zero-field splitting (ZFS) parameter for these complexes at physiological conditions and information on how this parameter is affected by interaction with lipids. Multifrequency EPR experiments at high magnetic fields are also useful in providing data on the frequency dispersion of electronic relaxation caused mainly by a modulation of the electron-electron dipolar interaction (ZFS) of these high spin ions.

Chelating Agents↗
PubMed1998

[Cryptic heterokaryons in Saccharomyces cerevisiae strains: pseudopleiotropic suppression in the multiple marked YPH857 strain].

The yeast strain YPH857 carrying multiple genetic markers was shown to segregate clones that had the pleiotropic suppression phenotype. The phenotype was designated Ppsu+. This suppression involves deletion alleles of the TRP1 and HIS3 genes and an insertion in the URA3 gene. Unlike the original YPH857 culture that carries an unidentified mutation of resistance to cycloheximide, the Ppsu+ clones exhibited a decreased level of resistance to this inhibitor of protein synthesis. In addition, they have a lower mating ability and can produce asci on a standard medium for sporulation. A comparative analysis of total DNA from the YPH857 strain and Ppsu+ segregants by Southern blotting provided evidence for the presence of an extraneous nucleus in these segregants. Ppsu+ strains were shown to contain wild-type alleles, apart from deletion and insertional alleles typical for the YPH857 strain. Moreover, they contain the 2 microns DNA of the Scp3 type with deletion of one of the two EcoRI and HpaI recognition sites (whereas the 2 microns DNA of YPH857 belongs to the Scp1 type) and exhibit heterogeneity with respect to the presence of one EcoR1 recognition site in the gene of 5S ribosomal RNA. It was supposed that the "cryptic" nucleus belongs to a strain of low viability and can survive as an unexpressed DNA in a small fraction of cells. Nuclei from the cryptic and YPH857 strains can be fused at a low rate to yield Ppsu+ cells capable of sporulation. In certain cases, a Ppsu+ clone may be heterogeneous: some of its cells contain nuclei in an unfused heterokaryotic state. This assumption has been confirmed by selecting Cyhr colonies with the original YPH857 genome among Ppsu+ clones on the cycloheximide-containing medium.

Cell Nucleus↗
PubMed1998

[Cryptic heterokaryons in Saccharomyces cerevisiae strains. Model experiments].

Heterokaryons capable of segregating clones of different phenotypes were obtained in saccharomycetes yeast. Clones expressing phenotypic traits encoded by the nuclear genome of one parent and the mitochondrial genome of another were shown to contain cells that carried the second phenotypically silent nucleus. The cryptic nucleus can be uncovered by growing these "cytoductants" on the corresponding medium. The use of strains carrying an insertion in the URA3 gene and the endogenic plasmid, 2 microns DNA, made it possible to detect this nucleus by blot hybridization.

Cell Nucleus↗
PubMed1997

Interaction of MRI gadolinium contrast agents with phospholipid bilayers as studied by 95 GHz EPR.

Interactions of two MRI gadolinium contrast agents, gadolinium ethoxybenzyl-diethylenetriaminepentaacetate (Gd-EOB-DTPA) and gadolinium N-pentyl-1,4,7,10-tetraazacyclododecane-N',N",N'"- triacetic acid (Gd-DOTA-P), with multibilayer phospholipid dispersions prepared from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) have been investigated with high resolution EPR spectroscopy at 95 GHz. At a resonance field of 3.3 T, EPR spectra of a small nitroxide probe, 2,2,6,6-tetramethyl-1-piperidinyloxyl (Tempo), partitioned between aqueous and membrane phases are clearly resolved, making measurements of dynamics parameters of the probe accurate and unambiguous. Results show that although the presence of the more lipophilic contrast agent, Gd-DOTA-P, can be detected within the bilayer, the structural organization of the membrane remains unaffected even at physiologically high (5 mM) concentrations. The temperature of the main phase transition of the bilayer was also unaffected to within the 0.4 degree C accuracy of its determination.

Contrast Media↗
PubMed1995

Accuracy of oxygen measurements in T2 (line width) EPR oximetry.

EPR oximetry is used for in vivo and in vitro measurements of oxygen in biological systems, including experimental animals. The accuracy of oxygen measurements in T2 (line width) EPR oximetry is significantly improved if least-squares simulation is used to extract the line width parameters. The oxygen effect on the EPR spectra of nitroxide solutions and aqueous suspensions of fusinite can be described as an additional homogeneous broadening that modifies the EPR spectrum of the oxygen-free probe. This allows one to use a one-parameter line width model in most cases. The simulations were carried out with the use of a fast-convolution algorithm followed by Levenberg-Marquardt optimization. The validity of error estimates provided by this method was tested on sets of experimental spectra taken under common conditions. It is shown that the accuracy of oxygen measurements in line width (T2) oximetry is determined not only by the probe sensitivity (rate of line width change versus oxygen concentration), but also by the signal-to-noise ratio, inhomogeneous contribution to the line shape (e.g., unresolved proton superhyperfine structure), and the spectral window. The accuracy of oxygen measurements is compared for aqueous solutions of two nitroxide radicals with different superhyperfine structure and for aqueous suspensions of fusinite.

Carbon↗
PubMed1995

Very high frequency electron paramagnetic resonance of 2,2,6,6-tetramethyl-1-piperidinyloxy in 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine liposomes: partitioning and molecular dynamics.

Partitioning and molecular dynamics of 2,2,6,6,-tetramethylpiperedine-1-oxyl (TEMPO) nitroxide radicals in large unilamellar liposomes (LUV) composed from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine were investigated by using very high frequency electron paramagnetic resonance (EPR) spectroscopy. Experiments carried out at a microwave frequency of 94.3 GHz completely resolved the TEMPO EPR spectrum in the aqueous and hydrocarbon phases. An accurate computer simulation method combined with Levenberg-Marquardt optimization was used to analyze the TEMPO EPR spectra in both phases. Spectral parameters extracted from the simulations gave the actual partitioning of the TEMPO probe between the LUV hydrocarbon and aqueous phases and allowed analysis of picosecond rotational dynamics of the probe in the LUV hydrocarbon phase. In very high frequency EPR experiments, phase transitions in the LUV-TEMPO system were observed as sharp changes in both partitioning and rotational correlation times of the TEMPO probe. The phase transition temperatures (40.5 +/- 0.2 and 32.7 +/- 0.5 degrees C) are in agreement with previously reported differential scanning microcalorimetry data. Spectral line widths were analyzed by using existing theoretical expressions for motionally narrowed nitroxide spectra. It was found that the motion of the small, nearly spherical, TEMPO probe can be well described by anisotropic Brownian diffusion in isotropic media and is not restricted by the much larger hydrocarbon chains existing in ripple structure (P beta') or fluid bilayer structure (L alpha) phases.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1990

[Changes in the level of tightly-bound mitochondrial phospholipids induced by exogenous factors].

The effects of some parameters of the incubation medium (tonicity, H+ and Pi concentration) on the phospholipid content in rat mitochondrial extracts prepared by normal extraction and by extraction with strongly acidified solvent mixtures, were studied. It was found that after normal extraction with a chloroform-methanol mixture, 8% to 25% of mitochondrial phospholipids can be additionally extracted by acidified solvent mixtures. The concentration of weakly extractable lipids depends on the tonicity and ionic composition of the incubation medium. It was suggested that there exist in mitochondria two lipid pools, a loosely and a tightly-bound ones; the equilibrium between these pools is effectively regulated by medium tonicity and other external factors.

Animals↗
PubMedDate not supplied

[Changes in hemispheric asymmetry under intensive foreign language instruction].

By means of dichotic listening test the study of perception dynamics was conducted in 20 persons during their intensive learning of French and German languages. Before the beginning of learning in all subjects, except three ones, the left hemisphere dominated in relation to verbal functions. In the process of learning in 84% of subjects activization of the opposite hemisphere was observed. In persons with the same initial level of language knowledge the success in colloquial practice was by expert evaluation as higher as bigger was the shift of the right ear coefficient at learning. The latter makes possible to evaluate quantitatively intellectual efforts spent in the process of learning. The authors suggest that such psychophysiological control of perception could be a support in solution of the problem of optimization of learning with the use of individual approach.

Adolescent↗