Evaluation of the professional qualities of operators working with computer displays

The influence of spatio-temporal factors (spatial heterogeneity of distribution of the numbers sought for in the matrix of data, processes of learning and development of fatigue, periodic attention oscillations) of the character of solving the task of searching the numbers in a matrix of 176 three-figure numbers (16 lines, 11 columns) was studied in 39 operators. The possibility was shown to use the characteristics obtained for evaluation of professionally important abilities of an operator working at the display.     

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.     

Anomalous change in the specific conductivity in lipoproteins at around physiologic temperatures

Studying the temperature dependence of conductivity sigma of rat and human lipoproteins and apoprotein A-I fractions revealed an anomalous region in the range of temperatures (35-38) +/- 0.5 degree C. The activation energy delta H and temperature coefficient sigma (delta sigma/delta T) on both sides of Tc and the heat of transition (delta H of transition) were calculated. In high-density human lipoproteins and apoA-I, the delta H value was found to be very low. Some mechanisms of interaction of hydrocortizone with high-density lipoproteins and apoA-I were studied by using IR-spectroscopy and conductometry were studied. It was found that the hormone considerably increases the portion of alpha-helices and beta-structures in these proteins (coil<-->alpha-helix and coil<-->beta-structure transitions). In this case, delta H value of the transition increases 13-fold; in addition, the abnormal region in apoA-I shifts 1-2 degrees C downwards. The anomalous changes in conductivity in the range of physiological temperatures in all lipoprotein fractions including apoA-I are probably related to structural phase transitions both in proteins and in phospholipids. Since the delta H value of the transition in human high-density lipoproteins is small, it is assumed that, in phospholipids of these particles, an orientation transition of the A<-->C smectic type takes place, which is assigned to the second-order phase transition. The structural transition in apoA-I can probably also be assigned to the second-order phase transition since the enthalpia of the transition is very small; presumably, this transition is related to changes in symmetry due to changes in the secondary structure (coil<-->beta-tructure transition).     

Diverse roles of eph receptors and ephrins in the regulation of cell migration and tissue assembly

Eph receptor tyrosine kinases and ephrins have key roles in regulation of the migration and adhesion of cells required to form and stabilize patterns of cell organization during development. Activation of Eph receptors or ephrins can lead either to cell repulsion or to cell adhesion and invasion, and recent work has found that cells can switch between these distinct responses. This review will discuss biochemical mechanisms and developmental roles of the diverse cell responses controlled by Eph receptors and ephrins.     

Study of the structural and structure-functional subdomains in the interphase nucleus by photostabilization

The role of the nuclear matrix components in the organization of structural and functional domains of interphase nuclei was studied using irradiation with blue light in the presence of a photosensibilized agent (Ethidium bromide). Nuclear domain resistance to extractive solution (2 M NaCl) treatment served as a criterion of irradiation-induced stabilization of different nuclear domains. The following results have been obtained: 1) the structural organization of the complexes of chromatin and clusters of replication does not depend on the state of the nuclear matrix in isolated nuclei; 2) chemical stabilization of the nuclear matrix by Cu(2+)-ions is not sufficient for the organization of chromatin domains; 3) irradiation in the presence of Ethidium bromide stabilizes domains of the nuclei, but does not lead to stabilization of the nuclear matrix internal network. Hence, the irradiation prevented extraction from the nuclear domains of nonhistone proteins which were not standard matrix proteins. Based on the results obtained, a hypothesis was proposed about a coexistence of two groups of nonhistone proteins in the cell nucleus. The first group includes proteins of the nuclear matrix involved in immobilization of scafford attachment regions and active genes. The second group includes some hypothetical structural proteins participating only in compaction of DNA of condensed chromatin.