Nucleomeric organization of chromatin

Chromatin in the nuclei fixed in tissue and in the nuclei isolated by low ionic strength solutions in the presence of Mg2+ is represented by globular (nucleomeric) fibrils, 20-25 nm in diameter. The staphylococcal or endogenous nuclear nuclease splits the chromatin fibrils resulting in fragments corresponding to nucleomers and their multimers. Upon removal of firmly bound Mg2+ the nucleomers unfold to form chains consisting of 4-6-8 nucleosomes. Mild hydrolysis of nuclear chromatin by staphylococcal nuclease results in a split-off of mono-, di- and trimers of nucleomers sedimenting in a sucrose density gradient in the presence of EDTA as particles with the sedimentation coefficients of 37, 47 and 55S, respectively. The sedimentation coefficient for the mononucleomer in a sucrose density gradient with MgCl2 is 45S. Determination of the length of DNA fragments of chromatin split-off by staphylococcal nuclease showed that the nucleomer consists of 8 nucleosomes, while the dimer and trimer of the nucleomer consists of 14-16 and 21-24 nucleosomes, respectively. The nucleomeric monomer undergoes structural transition from the compact (45S) to the "loose" state (37S) after removal of Mg2+. This transition is completely reversible, when the nucleomer contains histone H1. The removal of the latter or dialysis of the nucleomer against EDTA in low ionic strength solutions results in a complete unfolding of the nucleomer into a nucleosomal chain fragment. A model for the nucleomer fibril structure in which the helical organization of the nucleosomal chain in the nucleomer (2 turns with 4 nucleosomes in each) is alternated with the impaired helical bonds between the nucleomers is discussed. The functional significance of the nucleomeric organization of chromatin may be an additional restriction of the site-specific recognition of DNA in chromatin with the possibility of local (at the level of one nucleomer) changes in chromatin conformation excluding this restriction.     

Three-dimensional structure of the nickel-containing hydrogenase from Thiocapsa roseopersicina.

The three-dimensional structure of the nickel-containing hydrogenase from Thiocapsa roseopersicina has been determined at a resolution of 2 nm in the plane and 4 nm in the vertical direction by electron microscopy and computerized image processing on microcrystals of the enzyme. The enzyme forms a large ring-shaped complex containing six each of the large (62-kDa) and small (26-kDa) subunits. The complex is very open, with six well-separated dumbbell-shaped masses surrounding a large cylindrical hole. Each dumbbell is interpreted as consisting of one large and one small subunit.     

Vanadyl Causes Hydroxyl Radical Mediated Degradation of Deoxyribose

Vanadyl caused a time- and dose-dependent degradation of deoxyribose to carbonyl products detectable with thiobarbituric acid. This process was inhibited by catalase, ethanol or HEPES; whereas superoxide dismutase was without effect. Vanadate did not substitute for vanadyl even in the presence of a source of O₂^- plus H₂ O ₂; but it did so in the presence of reductants such as thiols or NADH. It appears that hydrogen peroxide, generated by the autoxidation of vanadyl, is reduced by vanadyl to the hydroxyl radical; which, in turn, was responsible for the degradation of deoxyribose. A similar process might contribute to the toxic and pharmacological effects of vanadium salts.     

Denatured increments of heat capacity in globular proteins and its connection with vitrification processes

Absolute values of heat capacity for some hydrated globular proteins have been studied by differential scanning calorimetry (DSC) method. It has been found that for the proteins with completely bound water, like in the case of protein solutions, the value of heat capacity of denatured proteins is higher than that prior to denaturation. Depending on temperature and humidity the denatured proteins can be either in high elastic or glass state. Specific heat capacities for these two states have the same values for all proteins and depend only on temperature with a characteristic increment of 0.55 J/g.K. at glass transition. The glass transitions were observed not only in denatured but also in native proteins. As it follows from our results, the main contribution to the heat capacity increment at denaturation is connected with the thermal motion in the protein globule which is in contrast with the commonly accepted ideas.     

Electric field increases the phase transition temperature in the bilayer membrane of phosphatidic acid

The effect of the electric field on the phase transition temperature (Tc) of acidic 1,2-dipalmitoyl-sn-glycero-3-phosphate (DPPA) and 1,2-dipalmitoyl-sn-glycero-3-thionphosphate (thion-DPPA) and zwitterion, i.e. 1,2-dipalmitoyl-rac-3-phosphocholine and 1,2-distearoyl-rac-glycero-3-phosphocholine (DPPC and DSPC), lipids has been investigated. The phase transition was detected using the jump-like increase effect in the conductance of the planar bilayer membrane. A voltage increase to 150 mV has been shown to increase the phase transition temperature in a bilayer lipid membrane (BLM) of phosphatidic acids (DPPA and thion-DPPA) by 8-12 degrees C while the transition temperature in the bilayer of zwitterion lipids (DPPC and DSPC) increases insignificantly. The increasing of Tt in BLM of acidic lipids is attributed to the voltage-induced changes in the molecule packing density.     

Chromosome polymorphism in populations of the grasshopper Trimerotropis pallidipennis from southern Argentina

Three populations of the grasshopper Trimerotropis pallidipennis from southern Argentina have been studied cytologically. A very characteristic B-chromosome was found in all three. They also showed geographical variability in respect of the presence of pericentric inversions, and the inversion system was found to influence chiasma frequency. The Laguna Blanca population, which is on the hypothetical pathway the species is believed to have followed during its migration from northern to southern latitudes, has the same karyotype composition as the N. American form, with fixed inversions in the 3 largest autosomes and the X-chromosome. Its members have a high total chiasma frequency and a great number of interstitial chiasmata. The Sierra de la Ventana population, situated at the absolute eastern border of the species distribution is highly polymorphic with respect to the presence of inversions in the medium chromosomes. Its members have the lowest total chiasma frequency and a greatly reduced number of interstitial chiasmata. Situated geographically between the other two, the Choele-Choel population has the highest frequency of inversions and many of them are homozygous. Its members have a higher total chiasma frequency than that observed in specimens from Sierra de la Ventana, and a greatly reduced number of interstitial chiasmata, similar to that observed in individuals from the latter population.     

Drug-induced immune tolerance to sheep erythrocytes in mice of different lines]

Immunological tolerance to sheep erythrocytes was induced in mice of the CBA, C57BL/6, CC57BR, C3H, DBA/2 lines by means of combined administration of a high dose of the antigen and cyclophosphamide. The count of 19S antibody-forming cells was determined in the mouse spleen after the test injection of erythrocytes, by local hemolysis in gel. The extent of the tolerance induced proved to depend on the genotype of the animals; mice of the DBA/2 line were found to be most "sensitive" to its induction. There was revealed no correlation between the level of the immunological reactivity to sheep erythrocytes in the intact mice of different lines and the extent of its suppression in tolerance induction     

Significance of endogenous glutathione in realizing the oxygen effect in bone marrow cells

It has been established using hemopoietic bone marrow cells or EHrlich ascites carcinoma cells that endogenous glutathione affects the realization of only those lesions which appear in response to an increase in radioresistance, for example during anoxia. The involvement of glutathione in the realization of the oxygen effect is not limited to the time of irradiation. The effect of glutathione extends to the postirradiation period i. e., it is not determined only by the competition with oxygen for target radicals.