1,817 research outputs found
Mechanical disengagement of the cohesin ring
Cohesin forms a proteinaceous ring that is thought to link sister chromatids by entrapping DNA and counteracting the forces generated by the mitotic spindle. Whether individual cohesins encircle both sister DNAs and how cohesin opposes spindle-generated forces remains unknown. Here we perform force measurements on individual yeast cohesin complexes either bound to DNA or holding together two DNAs. By covalently closing the hinge and Smc3Psm3âkleisin interfaces we find that the mechanical stability of the cohesin ring entrapping DNA is determined by the hinge domain. Forces of ~20âpN disengage cohesin at the hinge and release DNA, indicating that ~40 cohesin molecules are sufficient to counteract known spindle forces. Our findings provide a mechanical framework for understanding how cohesin interacts with sister chromatids and opposes the spindle-generated tension during mitosis, with implications for other force-generating chromosomal processes including transcription and DNA replication
Mechanical Design and Characteristics of a Superconducting Insertion Quadrupole Model Magnet for the Large Hadron Collider
A superconducting insertion quadruple is being developed by KEK in collaboration with CERN for the Large Hadron Collider (LHC) project. The mechanical design of the magnet in which the pre-stress is applied to the coil through thin stainless steel collars inside the yoke, the two halves of which are held together by means of keys, has been validated experimentally by measurements on a short model. The 140 mm long model was assembled from real magnet components in order to simulate the magnet assembly and to evaluate the change in coil pre-stress during assembly and cool-down. A new technique using capacitance pressure transducers was used, which has enabled measurements of the stress distributions in the coil with high accuracy. This paper describes the mechanical design of the quadrupole magnet and results obtained from the short mechanical model
Molecular motion in cell membranes: analytic study of fence-hindered random walks
A theoretical calculation is presented to describe the confined motion of
transmembrane molecules in cell membranes. The study is analytic, based on
Master equations for the probability of the molecules moving as random walkers,
and leads to explicit usable solutions including expressions for the molecular
mean square displacement and effective diffusion constants. One outcome is a
detailed understanding of the dependence of the time variation of the mean
square displacement on the initial placement of the molecule within the
confined region. How to use the calculations is illustrated by extracting
(confinement) compartment sizes from experimentally reported published
observations from single particle tracking experiments on the diffusion of
gold-tagged G-protein coupled mu-opioid receptors in the normal rat kidney cell
membrane, and by further comparing the analytical results to observations on
the diffusion of phospholipids, also in normal rat kidney cells.Comment: 10 pages, 5 figure
Dynamics of Arachidonic Acid Metabolism in Macrophages From DelayedâType Hypersensitivity (Schistosoma mansoni egg) and ForeignâBodyâType Granulomas
The present study examines the kinetics of arachidonic acid (AA) metabolism by murine macrophages isolated from sites of experimentally induced pulmonary granulomatous inflammation. Macrophages of Tâcellâmediated hypersensitivity lesions induced by Schistosoma mansoni eggs (SEâGM) and nonâTâcellâmediated foreignâbodyâtype lesions (FBâGM) induced by Sephadex beads were examined. Overall, macrophages from both types of lesions produced mainly lipoxygenase pathway metabolites, leukotrienes, and monohydroxyeicosatetraenoic acids (monoâHETEs). Early after induction (4 days [4D]), SEâGM showed an augmented zymosanâstimulated AA release and metabolism compared to resident peritoneal macrophages. Macrophages from mature lesions (8â32D) showed constitutive synthesis of metabolites and were refractory to zymosan stimulation. Both SEâGM and FBâGM showed augmented AA uptake incorporating a large proportion into neutral lipids. A direct comparison of SEâGM and FBâGM revealed that the Tâcellâmediated lesion produced lesser amounts of prostaglandins and leukotrienes and showed reduced incorporation of AA into phosphatidylcholine. These data suggest that AA metabolism by granuloma macrophages is sequentially modified during recruitment and activation at sites of chronic inflammation.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141165/1/jlb0671.pd
Quantum-well states in ultrathin Ag(111) films deposited onto H-passivated Si(111)-(1x1) surfaces
Ag(111) films were deposited at room temperature onto H-passivated
Si(111)-(1x1) substrates, and subsequently annealed at 300 C. An abrupt
non-reactive Ag/Si interface is formed, and very uniform non-strained Ag(111)
films of 6-12 monolayers have been grown. Angle resolved photoemission
spectroscopy has been used to study the valence band electronic properties of
these films. Well-defined Ag sp quantum-well states (QWS) have been observed at
discrete energies between 0.5-2eV below the Fermi level, and their dispersions
have been measured along the GammaK, GammaMM'and GammaL symmetry directions.
QWS show a parabolic bidimensional dispersion, with in-plane effective mass of
0.38-0.50mo, along the GammaK and GammaMM' directions, whereas no dispersion
has been found along the GammaL direction, indicating the low-dimensional
electronic character of these states. The binding energy dependence of the QWS
as a function of Ag film thickness has been analyzed in the framework of the
phase accumulation model. According to this model, a reflectivity of 70% has
been estimated for the Ag-sp states at the Ag/H/Si(111)-(1x1) interface.Comment: 6 pages, 6 figures, submitted to Phys. Rev.
Onchocerca volvulus heat shock protein 70 is a major immunogen in amicrofilaremic individuals from a filariasis-endemic area
Infestation with organisms causing lymphatic filariasis (i.e. Wuchereria bancrofti and Brugia malayi) results in a variety of clinical presentations. It is possible that some of the variation is due to differences in host response to parasite. To determine whether individuals who live in an endemic area but differ in their clinical manifestations respond to different filarial antigens, we screened Onchocerca volvulus expression libraries with sera from a number of individuals belonging to different clinical groups. The results of the study demonstrate that there are indeed differences in the recognition of three cloned filarial antigens and that this differential recognition is related to clinical symptomatology. The most striking finding is that an Onchocerca volvulus protein homologous to the 70 kDa Xenopus laevis heat shock protein is primarily recognized by individuals who are amicrofilaremic. Further analysis is required to determine whether these antigens play any role in the pathogenesis of filarial infection or have any potential value in protective immunity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28013/1/0000449.pd
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