Tethering Point Research Articles

Chain Retraction Potential in a Fixed Entanglement Network

When a chain, tethered at one end, is immersed in a fixed entanglement network, the mobile tip of the chain encounters an entropic potential barrier that penalizes deep fluctuations needed to bring the tip close to the tethering point. Using the tube model, Doi and Kuzuu [J. Polym. Sci., Polym. Lett. Ed. 18, 775 (1980)] estimated that this potential, which is crucial to describe the rheology of branched polymers in fixed networks and melts, has a quadratic form with a prefactor nu = 1.5. Later calculations based on regular lattices indicated that the potential is nonquadratic, and its steepness depends on the lattice coordination number. In this Letter, we analyze the primitive paths obtained using the bond-fluctuation model for chains with up to 12.5 entanglements. Our simulations confirm a quadratic form for the potential with a prefactor close to the Doi-Kuzuu value, nu approximately 1.5.

The Epstein-Barr Virus Replication Protein BBLF2/3 Provides an Origin-Tethering Function through Interaction with the Zinc Finger DNA Binding Protein ZBRK1 and the KAP-1 Corepressor

Herpesviruses encode a set of core proteins essential for lytic replication of their genomes. Three of these proteins form a tripartite helix-primase complex that, in the case of Epstein-Barr virus (EBV), consists of the helicase BBLF4, the primase BSLF1, and the linker protein BBLF2/3. BBLF2/3 and its homologs in the other herpesviruses remain relatively poorly characterized. To better understand the contribution to replication made by BBLF2/3, a yeast two-hybrid screen was performed with BBLF2/3 as the bait protein. This screen identified as interactors a number of cell replication-related proteins such as DNA polymerase beta and subunits of DNA polymerase delta along with the EBV-encoded DNase BGLF5. The screen also identified the DNA binding zinc finger protein ZBRK1 and the ZBRK1 corepressor KAP-1 as BBLF2/3 interactors. Interaction between BBLF2/3 and ZBRK1 and KAP-1 was confirmed in coimmunoprecipitation assays. A binding site for ZBRK1 in the EBV oriLyt enhancer was identified by electrophoretic mobility shift assay. ZBRK1, KAP-1, and the ZBRK1 binding protein BRCA1 were shown by indirect immunofluorescence to be present in replication compartments in lytically induced D98-HR1 cells, and additionally, chromatin immunoprecipitation assays determined that these proteins associated with oriLyt DNA. Replication of an oriLyt plasmid and a variant oriLyt (DeltaZBRK1) plasmid was examined in lytically induced D98-HR1 cells. Exogenous ZBRK1, KAP-1, or BRCA1 increased the efficiency of oriLyt replication, while deletion of the ZBRK1 binding site impaired replication. These experiments identify ZBRK1 as another cell protein that, through BBLF2/3, provides a tethering point on oriLyt for the EBV replication complex. The data also suggest that BBLF2/3 may serve as a contact interface for cell proteins involved in replication of EBV oriLyt.

Meningovenous structures of the petroclival region: clinical importance for surgery and intravascular surgery.

The goals of this investigation were to perform a detailed analysis of petroclival microanatomic features, to investigate the course of the abducens nerve in the petroclival region, and to identify potential causes of injury to neurovascular structures when anterior transpetrosal or transvenous endovascular approaches are used to treat pathological lesions in the petroclival region. Petroclival microanatomic features were studied bilaterally in seven cadaveric head specimens, which were injected with colored silicone before microdissection. Another cadaveric head was used for histological section analyses. A lateral or medial location of the abducens nerve dural entrance porus, relative to the midline, was correlated with the course and angulation of the abducens nerve in the petroclival region. The angulation of the abducens nerve was greater and the nerve was closer to the petrous ridge in the lateral type, compared with the medial type. The abducens nerve exhibited three changes in direction, which represented the angulations in the petroclival region, at the dural entrance porus, the petrous apex, and the lateral wall of the internal carotid artery. The abducens nerve was covered by the dural sleeve and the arachnoid membrane, which became attenuated between the second and third angulation points. The abducens nerve was anastomosed with the sympathetic plexus and fixed by connective tissue extensions to the lateral wall of the internal carotid artery and the medial wall of Meckel's cave at the third angulation point. There were two types of trabeculations inside the sinuses around the petroclival region (tough and delicate). The petroclival part of the abducens nerve was protected in a dural sleeve accompanied by the arachnoid membrane. Therefore, the risk of abducens nerve injury during petrous apex resection via the anterior transpetrosal approach, with the use of the transvenous route through the inferior petrosal sinus to the cavernous sinus, should be lower than expected. The presence of two anatomic variations in the course of the abducens nerve, in addition to findings regarding nerve angulation and tethering points, may explain the relationships between adjacent structures and the susceptibility to nerve injury with either surgical or endovascular approaches. Venous anatomic variations may account for previously reported cases of subarachnoid hemorrhage with the endovascular approach.

The Sprengel deformity

We evaluated scapular dysplasia and malposition in 15 patients with the Sprengel deformity using three-dimensional CT (3D-CT). The shape, height-to-width ratio, the areas of both scapulae, the anterior curvature of the supraspinous portion and glenoid version were assessed on scapular posterior, medial and inferior views. The degree of rotation and superior displacement were measured on the trunk posterior view. The omovertebral connection was also assessed and correlated with the operative findings. Most of the affected scapulae had a characteristic shape with a decrease in the height-to-width ratio and were larger than the contralateral scapulae. There was an inverse relationship between scapular rotation and superior displacement. The typical curve of the supraspinous portion of the scapula was seen in only three cases. There was no significant difference in glenoid version. The point of tethering of the omovertebral connection may determine the shape, rotation and superior displacement of the scapula. 3D-CT was helpful in delineating the deformity in detail, and in planning scapuloplasty.

The Sprengel deformity. Morphometric analysis using 3D-CT and its clinical relevance.

We evaluated scapular dysplasia and malposition in 15 patients with the Sprengel deformity using three-dimensional CT (3D-CT). The shape, height-to-width ratio, the areas of both scapulae, the anterior curvature of the supraspinous portion and glenoid version were assessed on scapular posterior, medial and inferior views. The degree of rotation and superior displacement were measured on the trunk posterior view. The omovertebral connection was also assessed and correlated with the operative findings. Most of the affected scapulae had a characteristic shape with a decrease in the height-to-width ratio and were larger than the contralateral scapulae. There was an inverse relationship between scapular rotation and superior displacement. The typical curve of the supraspinous portion of the scapula was seen in only three cases. There was no significant difference in glenoid version. The point of tethering of the omovertebral connection may determine the shape, rotation and superior displacement of the scapula. 3D-CT was helpful in delineating the deformity in detail, and in planning scapuloplasty.

Triphenylene-Based Discotic Liquid Crystals as Self-Assembled Monolayers

A series of ω-thiol-substituted 2,3,6,7,10,11-hexaalkoxytriphenylenes was synthesised for the purpose of forming self-assembled monolayers (SAMs) on gold in which the self-organizing, discogenic headgroups have a known orientation. In principle, these headgroups can be oriented either with their short axes perpendicular (disc “face-on”) on their short axes parallel (disc “edge-on”) to the surface, depending on the number and position of the tethering points. To obtain a “face-on” orientation of the headgroups a trithiol (three points of attachment) was synthesized and to obtain an “edge-on” orientation both monothiol and ortho-dithiol derivatives (one or two points of attachment) were made. Within the SAMs it was expected that the headgroups of the “face-on” discogen would self-organize into a hexagonal array and those of the “edge-on” discogens into columns that would run parallel to the surface. The kinetics of formation and the structures of the monolayers were characterized by contact angle measuremen...

Chemotaxis receptor recognition by protein methyltransferase CheR.

Signal transduction processes commonly involve reversible covalent modifications of receptors. Bacterial chemotaxis receptors are reversibly methylated at specific glutamate residues within coiled-coil regions of their cytoplasmic domains. Methylation is catalyzed by an S-adenosylmethionine-dependent protein methyltransferase, CheR, that binds to a specific sequence at the C-termini of some chemotaxis receptors. From this tethering point, CheR methylates neighboring receptor molecules. We report the crystal structure, determined to 2.2 A resolution, of a complex of the Salmonella typhimurium methyltransferase CheR bound to the methylation reaction product, S-adenosylhomocysteine (AdoHcy), and the C-terminal pentapeptide of the aspartate receptor, Tar. The structure indicates the basis for the specificity of interaction between the chemoreceptors and CheR and identifies a specific receptor binding motif incorporated in the CheR methyltransferase domain.

On the Structure and Pressure of Tethered Polymer Layers in Good Solvent

The structural and thermodynamic properties of tethered polymer chains in the good solvent regime are studied using the single-chain mean-field theory. The mushroom to brush transition is found to be broad. For surface coverages below the brush regime, i.e., mushroom regime and crossover region, the relevant length scale of the layers is found to be the bulk radius of gyration of the chains, R g , while in the brush regime the relevant length scale is the distance between tethering points as assumed in the analytical approaches. The onset of the brush regime corresponds to the beginning of the overlap between the chains as measured by the distance-dependent lateral radius of gyration of the chains. The predictions of the theory for the height of the polymer layer and the lateral pressures as a function of the surface coverage are compared with recent experimental observations of Kent and co-workers. Excellent agreement is found for the height of the brush for all surface coverages. The experimental lateral pressures multiplied by the square of the bulk radius of gyration are found to be a universal function of the reduced surface coverage, * =πR g 2 . The predictions of the theory are in good agreement with the experimental measurements up to values of the reduced surface coverages * ∼8. For higher reduced surface coverages the theoretical results deviate from the scaling found experimentally. This deviation is consistent with the fact that these surface coverages correspond to the brush regime. The theoretical lateral pressure is found to be better described as a universal function of * ∼8 from low to relatively high surface coverages. From the analysis of the average conformational properties of the chains, it is argued that the behavior of the measured lateral pressures at high reduced surface coverages may be due to nonequilibrium effects. From the comparisons between the theory and the experiments it is found that most of the measurements correspond to the crossover region between the mushroom and the brush regimes. This explains the scaling found for most experimental properties

Diffusion-controlled reactions on spherical surfaces. Application to bacteriophage tail fiber attachment

We have explored the kinetic implications of a model that may account for the acceleration of tail fiber (F) attachment to baseplates (B) by whiskers (W) on bacteriophage T4. The model assumes that a W-F complex is formed initially, and that the tethered fiber then undergoes rotational diffusion until a B-F encounter takes place. In the absence of whiskers, B-F complexes must form unassisted. Formation of a W-F intermediate will accelerate F attachment to B if (a) the bimolecular rate constant for W-F complex formation is larger than that for direct B-F interaction and (b) subsequent rotational diffusion of the tip of F to B is not much slower than the dissociation of W-F. Condition a was investigated by applying a recent theory of orientational effects on translational diffusion-controlled reactions. This theory suggests that substantial rate enhancement is expected if the reaction half-angle theta 0 is larger for W-F than for B-F complex formation. Condition b was investigated by calculating the mean and the variance of the time required for the diffusion of a molecule (the proximal tip of the fiber) on a spherical surface (whose radius is the distance from the tip to the whisker tethering point) into a circular sink (the baseplate site). The mean time is on the order of the inverse rotational diffusion coefficient, DR, of the fiber, but is sensitive to theta 0. Both conditions are satisfied for plausible choices of parameters. The solution to the diffusion equation we have obtained should have application to other physical situations, such as the rate of quenching of a fluorophore as it diffuses on the surface of a spherical membrane into proximity with a quencher.

Turbulence measurements over the sea by a tethered‐balloon technique

AbstractTurbulent fluctuations of wind, temperature and humidity at heights up to a few hundred metres have been measured over the open sea by instruments supported by a tethered balloon. Wave‐induced motion of the ship from which the balloon was flown produced unwanted contributions to the measured turbulence, but in light or moderate winds it has been possible to make allowances for these effects and to obtain useful estimates for vertical fluxes of heat and moisture: the calculated momentum fluxes in contrast appear less reliable and to obtain satisfactory values will require stabilization of the tethering point of the balloon cable. Some observations made in generally unstable conditions near OWS ‘J’ yield a value of (1.8 ± 0.7) × 10−3 for CE in the bulk aerodynamic formulation for evaporation (E = ρCE (q0 − q10)(U10 − U0)) and suggest that compared to the vertical moisture flux the heat flux may often have an insignificant rǒle in determining the buoyancy flux and hence the turbulence structure in the bulk of the boundary layer.