Evidence for UV-B-induced DNA degradation in Euglena gracilis mediated by activation of metal-dependent nucleases

It is demonstrated that in vivo irradiation with artificial UV-B for several hours significantly reduces the amount of large DNA extractable from immobilized Euglena in comparison with non-irradiated controls. This UV-B effect can be eliminated by a drastic reduction of the divalent ion concentration in the extracellular medium, i.e. the substitution of the culture medium by Tris-buffered agarose. Moreover, in vitro degradation of large DNA is demonstrated for crude protein extracts isolated from non-irradiated or UV-B-irradiated Euglena. The nuclease activity is shown for both crude protein extracts and purified nucleases; in both cases, two protein bands possessing nuclease activity are obtained with apparent molecular masses of 26 and 40 kDa and their activity is inhibited by specific nuclease inhibitors, i.e. aurintricarboxylic acid and ATP, applied at a concentration as low as 10(-8) M. Moreover, in vitro, nuclease activity clearly depends on the pH, with an optimum around pH 4.5, and on the ion composition of the extracellular medium. A strong stimulating effect is shown for Ca2+ with an optimum around 10(-4) M; this effect is potentiated by Zn2+ and Mn2+, but strongly counteracted by Mg2+ and the calmodulin inhibitors trifluoperazine and N- (6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W5). These results favour the concept which explains the lethal UV-B effect on Euglena as arising from a change in the general metabolic state of the cell and an activation of a DNA-degrading system, i.e. activation of metal-dependent nucleases (U.K. Tirlapur, D.-P. H?der and R. Scheuerlein, UV-B mediated damage in the photosynthetic flagellate, Euglena gracilis, studied by image analysis, Beitr. Biol. Pflanzen, 67 (1992) 305-317).     

Privacy and safety improvement of VANET data via a safety-related privacy scheme

International Journal of Information Security - Vehicular Ad-hoc NETwork (VANET) safety applications allow vehicles to exchange messages with surrounding vehicles periodically to improve the...     

Effectiveness of filter gabions against slope failure due to heavy rainfall

Slope failures due to heavy rainfall events are phenomena that can cause serious damage to social infrastructures and the loss of lives. Based on previous studies, natural slope failures are generally shallow and originate at the slope toe where infiltrated rainwater has accumulated and saturated it. Hence, it is extremely important to prevent these initial failures from inducing entire slope failures. In the present study, firstly, 1 g model tests, called G series tests, were conducted. In the tests, a gabion filled with filter materials was placed at the slope toe of each model for reinforcement and to drain the accumulated rainwater from the slope toe. Filter gabions have been found to shrink the failure regions and to significantly extend the time until slope failures occur. The failure mechanism in the G series tests was almost similar to that in cases without filter gabions if focus was placed on the slope above the filter gabions. However, the drainage effect was small. Secondly, P series tests, in which a filter gabion with a pipe was introduced for each model, were conducted. The results of these tests indicated that the displacements significantly decreased as the diameter of the pipe and the depth of the pipe’s insertion to the surface layer increased. Water did not discharge through the pipe until the pore water pressure around the pipe reached positive values. The failures always started when a phreatic surface appeared on the slope surface. Thus, it is very important to prevent a phreatic surface from forming on the slope surface. The adequate arrangement of a filter gabion with a drainage pipe may increase the potential for slope stability.