Inhibition of Mn2+-induced error-prone DNA synthesis with Cd2+ and Zn2+

Bivalent metal cations are key components in the reaction of DNA synthesis. They are necessary for all DNA polymerases, being involved as cofactors in catalytic mechanisms of nucleotide polymerization. It is also known that in the presence of Mn²⁺ the accuracy of DNA synthesis is considerably decreased. The findings of this work show that Cd²⁺ and Zn²⁺ selectively inhibit the Mn²⁺-induced error-prone DNA polymerase activity in extracts of cells from human and mouse tissues. Moreover, these cations in low concentrations also can efficiently inhibit the activity of homogeneous preparations of DNA polymerase iota (Pol ?), which is mainly responsible for the Mn²⁺-induced error-prone DNA polymerase activity in cell extracts. Using a primary culture of granular cells from postnatal rat cerebellum, we show that low concentrations of Cd²⁺ significantly increase cell survival in the presence of toxic Mn²⁺ doses. Thus, we have shown that in some cases low concentrations of Cd²⁺ can display a positive influence on cells, whereas it is widely acknowledged that this metal is not a necessary microelement and is toxic for organisms.     

Generation of zonal flows and large-scale magnetic fields by drift-Alfvén turbulence

The possibility of generating zonal perturbations by drift-Alfvén turbulence in a plasma with a finite pressure (1>β>m_e/m_i) is investigated. A set of coupled equations is derived that includes the equation for the spectral function of the turbulence and the averaged equations for zonal perturbations. It is shown that, in particular cases, the equation for the spectral function possesses action invariants; i.e., it takes the form of a conservation law for some quantities that are proportional to the spectral function of turbulence. Two types of instability of the zonal perturbations are revealed. The first type of instability generates only a zonal flow. Two regimes of this instability—resonant and hydrodynamic regimes—are examined, and the corresponding instability growth rates are determined. The second type of instability takes place when the resonant interaction of drift-Alfvén waves with electrons is taken into account. Because of this instability, the generation of a zonal magnetic field is inevitably accompanied by the generation of a zonal flow. It is found that the growth rate of the second type of instability is slower than that of the first type.     

Isolation and characterization of high affinity aptamers against DNA polymerase iota

Human DNA-polymerase iota (Pol ι) is an extremely error-prone enzyme and the fidelity depends on the sequence context of the template. Using the in vitro systematic evolution of ligands by exponential enrichment (SELEX) procedure, we obtained an oligoribonucleotide with a high affinity to human Pol ι, named aptamer IKL5. We determined its dissociation constant with homogenous preparation of Pol ι and predicted its putative secondary structure. The aptamer IKL5 specifically inhibits DNA-polymerase activity of the purified enzyme Pol ι, but did not inhibit the DNA-polymerase activities of human DNA polymerases beta and kappa. IKL5 suppressed the error-prone DNA-polymerase activity of Pol ι also in cellular extracts of the tumor cell line SKOV-3. The aptamer IKL5 is useful for studies of the biological role of Pol ι and as a potential drug to suppress the increase of the activity of this enzyme in malignant cells.     

Analytical solutions for global geodesic acoustic modes in tokamak plasmas

Analytical solutions for global geodesic acoustic modes in the plasma of a tokamak with circular concentric magnetic surfaces are obtained. In the framework of ideal magnetohydrodynamics, an integral equation for eigenvalues (dispersion relation) taking into account toroidal coupling between electrostatic perturbations and electromagnetic perturbations with the poloidal mode number |m| = 2 is derived. In the absence of such coupling, the dispersion relation yields only the standard continuous spectrum. The existence of a global geodesic acoustic mode is analyzed for equilibria with both on-axis and off-axis maxima of the local geodesic acoustic frequency. The analytical results are compared with results of numerical calculations.     

Generation of large-scale structures by strong drift turbulence

The previously existing quasilinear theory of the generation of a large-scale radial electric field by small-scale drift turbulence in a plasma is generalized for the case of strong turbulence which is usually observed in experiments. The geostrophic equation (i.e., the reduced Charney-Hasegawa-Mima equation) is used to construct a systematic theory in the two-scale direct interaction approximation. It is shown that, as in the quasilinear case, drift turbulence results in a turbulent viscosity effect and leads to the renormalization of the Poisson bracket in the Charney-Hasegawa-Mima equation. It is found that, for strong drift turbulence, the viscosity coefficient is represented as a sum of two parts, which are comparable in magnitude. As in quasilinear theory, the first part is determined by the second-order correlation functions of the turbulent field and is always negative. The second part is proportional to the third-order correlation functions, and the sign of its contribution to the turbulent viscosity coefficient depends strongly on the turbulence spectrum. The turbulent viscosity coefficient is calculated numerically for the Kolmogorov spectra, which characterize the inertial interval of the drift turbulence.     

Long-wavelength instability of periodic flows and helicon waves in electron magnetohydrodynamics

The stability of periodic flows and helicon waves against large-scale perturbations is investigated analytically in resistive electron magnetohydrodynamics by the method of two-scale expansions. It is shown that long-wavelength perturbations of a Kolmogorov-type flow are destabilized by the effect of negative resistivity. The destabilization of long-wavelength perturbations of a Beltrami-type helical flow and helicon waves is related to the microhelicity of the primary flow (wave). The instability of long-wavelength perturbations of an anisotropic helical flow is found to result from both the effect of negative resistivity and the effect associated with the microhelical nature of the flow. The criteria for the onset of the corresponding instabilities are derived. Numerical simulations are carried out based on nonlinear electron magnetohydrodynamic equations with initial conditions corresponding to the analytic formulation of the problem. The results of simulations on the whole confirm analytical results in the parameter range in which the latter are applicable and, in addition, extend the stability analysis to the parameter ranges that are beyond the scope of analytic approximations.     

Geodesic acoustic modes in noncircular cross section tokamaks

The influence of the shape of the plasma cross section on the continuous spectrum of geodesic acoustic modes (GAMs) in a tokamak is analyzed in the framework of the MHD model. An expression for the frequency of a local GAM for a model noncircular cross section plasma equilibrium is derived. Amendments to the oscillation frequency due to the plasma elongation and triangularity and finite tokamak aspect ratio are calculated. It is shown that the main factor affecting the GAM spectrum is the plasma elongation, resulting in a significant decrease in the mode frequency.     

Low-Frequency Continuous MHD Spectrum of Toroidally Rotating Tokamak Plasmas with Anisotropic Pressure

Plasma Physics Reports - Continuous-spectrum equations for low-frequency ideal magnetohydrodynamic perturbations in toroidally rotating plasmas with anisotropic pressure in axisymmetric tokamaks...     

Discharge Oscillations in Morozov’s Stationary Plasma Thruster as a Manifestation of Large-Scale Modes of Gradient Drift Instability

Plasma Physics Reports - The phenomenon of large-scale discharge oscillations in Morozov’s stationary plasma thruster (SPT) is physically interpreted by analyzing global modes of gradient...