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A D Gruzdev

Publications and source records attributed to A D Gruzdev.

At least 19 recordsLinked to original sources
PubMed1992

Topological state of DNA in polytene chromosomes.

A new microfluorometric method was developed for measuring two topological characteristics of DNA in isolated nuclei, chromosomes and other DNA containing structures: (1) the relative amount of the topologically non-closed DNA (tncDNA) and (2) the supercoiling density of the topologically closed unconstrained DNA (tcDNA). The method was applied to isolated polytene nuclei and chromosomes of Chironomus thummi. The relative amount of tncDNA was found to be 0.21. Evidence in favour of the tncDNA localization in transcriptionally active loci (puffs) of the polytene chromosomes is presented. The supercoiling density of tcDNA localized, presumably, in inactive loci (bands) of the polytene chromosomes is about -0.001.

Animals↗
PubMed1991

Functional and structural units in the chromomere.

Electron microscopic observations demonstrate the existence of several DNA packing levels in the chromomere. A linear DNA molecule forms a big (chromomere) loop anchored to the chromosomal scaffold. The loop forms a set of smaller loops in the rosette pattern. Packing of the DNA by the histone octamer particles results in nucleosomes and nucleomeres. To establish the possible correspondence between the structural units of a chromomere and the genetical units (genes, exons, introns) in it, we compared the lengths of the units. Statistical analysis of the 315 sequenced genes indicate that the average gene size corresponds to the average length of a rosette loop. It means that a chromomere contains one or more genes. Assuming that exon-intron boundaries cannot bind nucleosomes we constructed DNA-packing models of the 88 genes. They demonstrate that the first (in 77.8 per cent of the genes) and the last (in 52.7 per cent) exons of the genes are too short to bind nucleosomes. Many genes contain long (nucleosome binding) pieces of DNA. Long packed pieces are introns in vertebrates; they are exons in invertebrates and plants. The average size gene contains two nucleomeres.

Animals↗
PubMed1989

[Changes in the cellular structure of the salivary glands in Chironomus larvae resulting from mechanical cell damage].

Rapid morphological changes were observed in some cells of hand-isolated salivary glands of Ch. thummi larvae. The nuclear envelope, routinely closely fitting the tightly packaged polytene chromosomes, was seen to lose its contact with the chromosomes and to attain a smooth round shape. Then unfolding of the chromosomes occurred, their banding patterns becoming clearly evident, probably through widening the interband regions; the chromosome length increased by about 20%. We argue that the changes observed were induced during gland isolation by lesions of the cell basal envelope in the sites of the fat body connections to the salivary gland.

Animals↗
PubMed1984

Fluorescence polarization study of tertiary structure of DNA within bacteriophage lambda.

The fluorescence polarization of acridine orange-stained, oriented lambda phages was measured. The parameters of DNA packing within the phage head cos2 theta and cos4 theta were calculated (theta, angle between the direction of a small segment of DNA and the phage axis). It is shown that simple models of lambda phage DNA tertiary structure are not consistent with calculated values. A new model is proposed.

Acridine Orange↗
PubMed1980

[Evidence of single-strandedness in eukaryotic chromosomes].

Polytene salivary gland chromosomes of Chironomus thummi were stretched in pronase solution by 176 +/- 26 times up to their break (fig. 1). The DNA packed arrangement coefficient, determined as a ratio of DNA length, equal to 85 +/- 5 mm in a haploid set, to the length of 520 +/- 40 microns of a set of polytene chromosomes was found to be 164 +/- 22. The coincidence of these two values is a very strong evidence in favour of the uninemity of chromatids of the Chironomus chromosomes. The effect of ethidium bromide on elastic properties of chromosomes, preliminary stretched in pronase (fig. 2), and the lengthening of these chromosomes after ethidium staining prove that DNA molecules are double-stranded and supercoiled until chromosomes are broken. This enables us to conclude that each chromatid of Chironomus consists of a single DNA molecule or, more probably, of a single chain of linked DNA molecules whose both ends are located in telomeres of chromosomes.

Animals↗
PubMed1980

[Model of chromonema packing in the mitotic chromosome].

Based on available data, a model of packing of a chromonemata in mitotic chromosomes is presented (fig. 1). The model reflects three well established facts: 1) chromosomes are uninemic, i.e. each chromonema consists of a single DNA molecule (or a single chain of linked DNA molecules), whose ends are located in telomeres; 2) a proteinaceous fibre is a structural basis of a chromatid; the fibre is folded, its ends are located near a centromere; 3) a chromonema makes a spiral in the chromatid. The model reveals half-chromatid structure of mitiotic chromosomes and may describe morphological changes of chromosomes induced by substances affecting the states of chromonemata or fibres.

Animals↗
PubMed1979

[Nonhomogeneity of the distribution of the absorbing substance in cytophotometry].

Results of two-wavelengths cytophotometry may be used to calculate m--the quantity of light absorbing substance, and gamma--the degree of non-homogeneity of distribution of the substance on a preparation. Formula (1) is almost free from any distributional error. Optical density limits of applicability of formula (3) for gamma are shown on fig. 2. An algorithm for calculation of gamma at higher optical densities is proposed.

Absorption↗
PubMed1978

Fluorescence polarization of stretched polytene chromosomes stained with acridine orange.

The molecules of the fluorescent dye acridine orange (AO) bind to DNA in such a way that the absorption and emission dipoles lie on a plane perpendicular to the DNA axis. For this reason, definite fluorescence polarization should correspond to each mode of spatial DNA packing. A chromosome, considered as an axially symmetrical ensemble of DNA, was characterized by two experimental parameters, P parallel and P perpendicular, i.e., by polarizations of fluorescence excited by light polarized parallel and perpendicular to the symmetry axis. In view of the sequential order in the packing levels of DNA fiber in a chromosome, it was suggested that, under mechanical stretching, the highest level is disrupted first, then the others, in the order of their sequence. Isolated chromosomes of Chironomus thummi were stained with AO and stretched with needles of a micromanipulator. From the changes of P parallel and P perpendicular measured during stretching it was concluded the polytene chromosome bands have three, at least, DNA packing levels, tentatively described as 100 A fiber, 250 A coil and chromomere.

Acridines↗
PubMed1978

[Preparation and properties of stretched polytene chromosomes. 2. Mechanism of stretching].

Isolated polytene chromosomes were stretched in a 0.125 M NaCl solution with constant speed, by constant force and by cyclically changing force. For each regime, the dependence of chromosome length on the time and force magnitude were recorded. From this it may be concluded that three processes are involved in chromosome stretching: viscoelastic deformation, viscous flow of DNP segments, and cristallization, i.e. intermolecular cross-linking of neighbour segments. At a high rate stretching (V greater than Vo) chromosome may be torn like at small deformation; when rate is V greater than Vo chromosome deformation is mostly viscoelastic; at rates V approximately Vo viscous flow of DNP segments if predominant. We estimate Vo approximately less than 3--6 mum/s. Electron microscopy shows that during chromosome stretching its DNP fibers are oriented along chromosome axis without detectable breaks.

Animals↗
PubMed1977

[Preparation and properties of elongated polytene chromosomes. I. The method].

Compactness of eukaryotic, particularly polytene chromosomes pose difficulties for investigation of their functional organization. For example, 0.1 --1.0 micrometer thick bands of polytene chromosomes contain some dozens microns pieces of DNA molecules. Therefore the useful resolving power of autoradigraphical methods is reduced by 10--100 times of its upper limit. To overcome the mentioned difficulty, a new method has been developed which permits to attain the upper limit of resolution. An isolated polytene chromosome from salivary gland nucleus of Chironomus thummi larva is stretched by microneedles to obtain a bundle of oriented DNP-fibers. A previously chosen small region of the chromosome (band or puff) is stretched simultaneously in a transverse direction by a stick frame made of another chromosome. Electron microscopy of the preparation reveals a meshwork of DNP fibers as presented on fig. 6.

Animals↗
PubMed1976

[Cytogenetic effect of ultraviolet rays in mammalian cells at the DNA synthesis stage].

The frequency of chromosome aberrations induced by UV light at various wavelengths in the primary culture of mouse embryonic fibroblasts during the S-phase was studied. The aberration frequency is wavelength-dependent and reaches a maximum at 265 nm. The action spectrum for the chromosome aberrations determined at 254, 265, 280 and 302 nm closely conforms to the absorption spectra of thymidine. The value of caffeine potentiation was the same for 265 and 280 nm UV-induced aberrations. This indicates that primary chromosome damages and their transformation in cells are similar at these two wavelengths. The data obtained suggest that the formation of DNA cross-links following thymine dimerization is the first step in the formation of UV-induced chromosome aberrations in mammalian cells at the S phase.

Caffeine↗
PubMed1975

[Stretched polytene chromosomes--model for studying the functional organization of eukaryotic chromosomes].

To localize functional loci on cytological maps of polytene chromosomes we propose to use 10-100 times stretched chromosomes. Three different ways of stretchening are briefly considered: the squash tissue preparation, when chromosomes are stretched by hydrodynamical forces; the treatment of isolated polytene chromosomes in 10-minus 4M EDTA OR 0.8M NaCL with subsequent change of these solution for saline when abrupt structural changes occur in chromosomes and they become morphologically homogeneous threads (Gruzdev and Belaya, 1973); and, finally, the use of microneedles of the micromanipulator. After an intense (ca. 100 times) stretchening, the autoradiography is sufficient to localize the loci within one micron length of double helical DNA molecule.

Chromosome Mapping↗