H Ohlenbusch | PubMed Health

PubMed1990

DNA rotational positioning in a regulatory nucleosome is determined by base sequence. An algorithm to model the preferred superhelix.

MMTV-LTR sequences -190/-45 position a histone octamer both in vivo and in vitro. Experimental evidence suggested that nucleosome rotational positioning is determined by the DNA sequence itself. We developed an algorithm that is able to predict the most favorable path of a given DNA sequence over a histone octamer, based on rotational preferences of different dinucleotides. Our analysis shows that these preferences are sufficient for explaining the observed rotational positioning of the MMTV-LTR nucleosome, at one base pair accuracy level. Computer-generated 3-D models of the experimentally calculated and predicted MMTV-LTR nucleosome show that the predicted orientation is fully compatible with the currently available data in terms of accessibility of relevant sequences to regulatory proteins.

Algorithms↗

PubMed1987

Temperature-dependence of red cell aggregation.

To investigate the temperature-dependence of red cell aggregation 20 blood samples of normal donors and 20 blood samples of patients with venous ulcers of the leg were examined by photometric aggregometry at 3 degrees C, 10 degrees C, 20 degrees C, 30 degrees C and 37 degrees C. With decreasing temperature red cell aggregates become more resistant to hydrodynamic dispersion and they become more prone to growing under low shear stress. It is concluded that a decrease in temperature causes an increase in adsorptive energy of red cell aggregation, which is most likely due to an increase in molecular adsorption stress. Red cell aggregate formation as an overall process is retarded by a decrease in temperature, which is primarily due to an increase in plasma viscosity causing increased damping of aggregate formation. Accordingly the rate constant of aggregate formation corrected for plasma viscosity increases with decreasing temperature. The temperature-dependence of the kinetic parameters can be explained by a theoretical model that suggests the increase in contact area between aggregating red blood cells as the rate-limiting step of red cell aggregation. As a whole red cell aggregation is favoured by lowering of temperature.

Erythrocyte Aggregation↗