Crimean-Congo Hemorrhagic Fever in Turkey

Nineteen cases of suspected Crimean-Congo hemorrhagic fever reported from Turkey

Large-Scale Structure of Chromatin: A Fractal Globule or a Logarithmic Fractal?

Two physical models are considered to describe the large-scale structure of chromatin in the nucleus of a biological cell in the interphase state: a fractal globule model and a logarithmic fractal model. Based on the classification of fractal objects developed by the small-angle neutron scattering (SANS) method, it is shown that the fractal globule model does not satisfy the experimental data on small-angle neutron scattering by the nuclei of biological cells. Conversely, the logarithmic fractal model well describes the experimental data on SANS and, hence, provides a good approximation to describe the large-scale structure of chromatin. The logarithmic fractal model predicts that the nuclear space is exactly half-filled with chromatin, and the second half consists of interchromatin voids filled with nucleoplasma in which various nuclear processes occur. Thus, two opposing trends are balanced in the structural organization of chromatin: an increase in the surface area of chromatin in the cell nucleus (accessibility to external agents) and a decrease in the volume occupied by chromatin (compactness of the nucleus)

On the Nature of Defects in Mn1 –xFexGe Compounds Synthesized under High Pressure

The mesostructure of Mn1 – xFex Ge transition-metal monogermanides is studied by small-angle neutron scattering (SANS) and ultra-SANS in a wide concentration range of x = 0.0–1.0.It is shown that the main contribution to the scattering intensity for all concentrations x is made by scattering at crystallites with sharp boundaries and sizes of 1–10 μm, which is described by the squared Lorentzian function. An additional contribution to the scattering intensity as a result of scattering at an ensemble of defects is found as well, which is characteristic of manganese-rich samples. This contribution is well fitted by the power function Q–n with the exponent n = 3. The complementary scattering typical of iron-rich samples is described by an exponential function and also seems to be a part of scattering at sharp-boundary crystallites

Switch of fractal properties of DNA in chicken erythrocytes nuclei by mechanical stress

The small-angle neutron scattering (SANS) on the chicken erythrocyte nuclei demonstrates the bifractal nature of the chromatin structural organization. Use of the contrast variation (D2O−H2O) in SANS measurements reveals the differences in the DNA and protein arrangements inside the chromatin substance. It is the DNA that serves as a framework that constitutes the bifractal behavior showing the mass fractal properties with D=2.22 at a smaller scale and the logarithmic fractal behavior with D≈3 at a larger scale. The protein spatial organization shows the mass fractal properties with D≈2.34 throughout the whole nucleus. The borderline between two fractal levels can be significantly shifted toward smaller scales by centrifugation of the nuclei disposed on the dry substrate, since nuclei suffer from mechanical stress transforming them to a disklike shape. The height of this disk measured by atomic force microscopy (AFM) coincides closely with the fractal borderline, thus characterizing two types of the chromatin with the soft (at larger scale) and rigid (at smaller scale) properties. The combined SANS and AFM measurements demonstrate the stress induced switch of the DNA fractal properties from the rigid, but loosely packed, mass fractal to the soft, but densely packed, logarithmic fractal

Observation of nucleic acid and protein correlation in chromatin of HeLa nuclei using small-angle neutron scattering with D 2 O − H 2 O contrast variation

The small-angle neutron scattering (SANS) on HeLa nuclei demonstrates the bifractal nature of the chromatin structural organization. The border line between two fractal structures is detected as a crossover point at Qc≈4×10−2nm−1 in the momentum transfer dependence Q−D. The use of contrast variation (D2O−H2O) in SANS measurements reveals clear similarity in the large scale structural organizations of nucleic acids (NA) and proteins. Both NA and protein structures have a mass fractal arrangement with the fractal dimension of D≈2.5 at scales smaller than 150 nm down to 20 nm. Both NA and proteins show a logarithmic fractal behavior with D≈3 at scales larger than 150 nm up to 6000 nm. The combined analysis of the SANS and atomic force microscopy data allows one to conclude that chromatin and its constitutes (DNA and proteins) are characterized as soft, densely packed, logarithmic fractals on the large scale and as rigid, loosely packed, mass fractals on the smaller scale. The comparison of the partial cross sections from NA and proteins with one from chromatin as a whole demonstrates spatial correlation of two chromatin's components in the range up to 900 nm. Thus chromatin in HeLa nuclei is built as the unified structure of the NA and proteins entwined through each other. Correlation between two components is lost upon scale increases toward 6000 nm. The structural features at the large scale, probably, provide nuclei with the flexibility and chromatin-free space to build supercorrelations on the distance of 103 nm resembling cycle cell activity, such as an appearance of nucleoli and a DNA replication