84,803 research outputs found

    The steady-state repertoire of human SCF Ubiquitin ligase complexes does not require ongoing Nedd8 conjugation

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    The human genome encodes 69 different F-box proteins (FBPs), each of which can potentially assemble with Skp1-Cul1-RING to serve as the substrate specificity subunit of an SCF ubiquitin ligase complex. SCF activity is switched on by conjugation of the ubiquitin- like protein Nedd8 to Cul1. Cycles of Nedd8 conjugation and deconjugation acting in conjunction with the Cul1-sequestering factor Cand1 are thought to control dynamic cycles of SCF assembly and disassembly, which would enable a dynamic equilibrium between the Cul1- RING catalytic core of SCF and the cellular repertoire of FBPs. To test this hypothesis, we determined the cellular composition of SCF complexes and evaluated the impact of Nedd8 conjugation on this steady-state. At least 42 FBPs assembled with Cul1 in HEK 293 cells, and the levels of Cul1-bound FBPs varied by over two orders of magnitude. Unexpectedly, quantitative mass spectrometry revealed that blockade of Nedd8 conjugation led to a modest increase, rather than a decrease, in the overall level of most SCF complexes. We suggest that multiple mechanisms including FBP dissociation and turnover cooperate to maintain the cellular pool of SCF ubiquitin ligases

    Superfluid-Superfluid Phase Transitions in Two-Component Bose System

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    Depending on the Hamiltonian parameters, two-component bosons in an optical lattice can form at least three different superfluid phases in which both components participate in the superflow: a (strongly interacting) mixture of two miscible superfluids (2SF), a paired superfluid vacuum (PSF), and (at a commensurate total filling factor) the super-counter-fluid state (SCF). We study universal properties of the 2SF-PSF and 2SF-SCF quantum phase transitions and show that (i) they can be mapped onto each other, and (ii) their universality class is identical to the (d+1)-dimensional normal-superfluid transition in a single-component liquid. Finite-temperature 2SF-PSF(SCF) transitions and the topological properties of 2SF-PSF(SCF) interfaces are also discussed.Comment: 4pages, 2 figures, REVTe

    Friction and wear of single-crystal and polycrystalline maganese-zinc ferrite in contact with various metals

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    Sliding friction experiments were conducted with single-crystal (SCF) and hot-pressed polycrystalline (HPF) manganese-zinc ferrite in contact with various metals. Results indicate that the coefficients of friction for SCF and HPF are related to the relative chemical activity of those metals in high vacuum. The more active the metal, the higher the coefficient of friction. The coefficients of friction for both SCF and HPF were the same and much higher in vacuum than in argon at atmospheric pressure. All the metals tested transferred to the surface of both SCF and HPF in sliding. Both SCF and HPF exhibited cracking and fracture with sliding. Cracking in SCF is dependent on crystallographic characteristics. In HPF, cracking depends on the orientation of the individual crystallites

    WAGES in CANADA: SCF, SLID, LFS and the Skill Premium

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    For the years 1981 to 1997 the Survey of Consumer Finances served as the main source of information about the earnings of individuals, households and families. The Survey of Labour Income Dynamics, begun in 1993, was intended to replace and to improve upon the SCF. The Labour Force Survey which began releasing earnings information in 1997 (the last year of the SCF) is a second alternative for extending historical earnings data to the present day. This paper examines the extent to which either of these two surveys can be used to extend the SCF series to more recent times. Neither survey comes off as satisfactory in all respects as an extension of SCF earnings data though if one's purposes are more limited, such as studying the education premium, then merging results from the SCF and SLID seems a reasonable way to proceed. It is not possible here to assess the ability of SLID or LFS to extend the SCF for other applications. But this method could easily be adapted to address other similar questions.earnings; education premium; SLID; SCF
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