PACemakers of proteasome core particle assembly

The 26S proteasome mediates ubiquitin-dependent proteolysis in eukaryotic cells. A number of studies including very recent ones have revealed that assembly of its 20S catalytic core particle is an ordered process that involves several conserved proteasome assembly chaperones (PACs). Two heterodimeric chaperones, PAC1-PAC2 and PAC3-PAC4, promote the assembly of rings composed of seven alpha subunits. Subsequently, P subunits join to form half-proteasome precursor complexes containing all but one of the 14 subunits. These complexes lack the beta 7 subunit but contain UMP1, another assembly chaperone, and in yeast, at least to some degree, the activator protein Blm10. Dimerization of two such complexes is triggered by incorporation of beta 7, whose C-terminal extension reaches out into the other half to stabilize the newly formed 20S particle. The process is completed by the maturation of active sites and subsequent degradation of UMP1 and PAC1-PAC2.Fundacao para a Ciencia e Tecnologia; Deutsche Forschungsgemeinschaf

Performance Pay and Multidimensional Sorting - Productivity, Preferences and Gender

This paper studies the impact of incentives on worker self-selection in a controlled laboratory experiment. Subjects face the choice between a fixed and a variable payment scheme. Depending on the treatment, the variable payment is a piece rate, a tournament or a revenue-sharing scheme. We find that output is higher in the variable pay schemes (piece rate, tournament, and revenue sharing) compared to the fixed payment scheme. This difference is largely driven by productivity sorting. In addition personal attitudes such as willingness to take risks and relative self-assessment as well as gender affect the sorting decision in a systematic way. Moreover, self-reported effort is significantly higher in all variable pay conditions than in the fixed wage condition. Our lab findings are supported by an additional analysis using data from a large and representative sample. In sum, our findings underline the importance of multi-dimensional sorting, i.e., the tendency for different incentive schemes to systematically attract people with different individual characteristics

How people know their risk preference

People differ in their willingness to take risks. Recent work found that revealed preference tasks (e.g., laboratory lotteries)—a dominant class of measures—are outperformed by survey-based stated preferences, which are more stable and predict real-world risk taking across different domains. How can stated preferences, often criticised as inconsequential “cheap talk,” be more valid and predictive than controlled, incentivized lotteries? In our multimethod study, over 3,000 respondents from population samples answered a single widely used and predictive risk-preference question. Respondents then explained the reasoning behind their answer. They tended to recount diagnostic behaviours and experiences, focusing on voluntary, consequential acts and experiences from which they seemed to infer their risk preference. We found that third-party readers of respondents’ brief memories and explanations reached similar inferences about respondents’ preferences, indicating the intersubjective validity of this information. Our results help unpack the self perception behind stated risk preferences that permits people to draw upon their own understanding of what constitutes diagnostic behaviours and experiences, as revealed in high-stakes situations in the real world

Extreme magnesium isotope fractionation at outcrop scale records the mechanism and rate at which reaction fronts advance

Isotopic fractionation of cationic species during diffusive transport provides novel means of constraining the style and timing of metamorphic transformations. Here we document a major (~1‰) decrease in the Mg isotopic composition of the reaction front of an exhumed contact between rocks of subducted crust and serpentinite, in the Syros mélange zone. This isotopic perturbation extends over a notable length-scale (~1 m), implicating diffusion of Mg through an intergranular fluid network over a period of ~100 kyr. These novel observations confirm models of diffusion-controlled growth of reaction zones formed between rocks of contrasting compositions, such as found at the slab-mantle interface in subduction zones. The results also demonstrate that diffusive processes can result in exotic stable isotope compositions of major elements with implications for mantle xenoliths and complex intrusions

Hsp70 and Hsp110 chaperones promote early steps of proteasome assembly

Whereas assembly of the 20S proteasome core particle (CP) in prokaryotes apparently occurs spontaneously, the efficiency of this process in eukaryotes relies on the dedicated assembly chaperones Ump1, Pba1-Pba2, and Pba3-Pba4. For mammals, it was reported that CP assembly initiates with formation of a complete alpha-ring that functions as a template for beta subunit incorporation. By contrast, we were not able to detect a ring composed only of a complete set of alpha subunits in S. cerevisiae. Instead, we found that the CP subunits alpha 1, alpha 2, and alpha 4 each form independent small complexes. Purification of such complexes containing alpha 4 revealed the presence of chaperones of the Hsp70/Ssa and Hsp110/Sse families. Consistently, certain small complexes containing alpha 1, alpha 2, and alpha 4 were not formed in strains lacking these chaperones. Deletion of the SSE1 gene in combination with deletions of PRE9 (alpha 3), PBA3, or UMP1 genes resulted in severe synthetic growth defects, high levels of ubiquitin-conjugates, and an accumulation of distinct small complexes with alpha subunits. Our study shows that Hsp70 and Hsp110 chaperones cooperate to promote the folding of individual alpha subunits and/or their assembly with other CP subunits, Ump1, and Pba1-Pba4 in subsequent steps.info:eu-repo/semantics/publishedVersio

Li–Na interdiffusion and diffusion-driven lithium isotope fractionation in pegmatitic melts

In this study, we investigate the diffusion of Li and its stable isotopes (6Li and 7Li) in flux-rich (1.8 % Li2O, 2.6 % B2O3, 2.3 % P2O5 and 3 % F) pegmatitic melts in order to contribute to the understanding of Li enrichment in such systems. Two glasses were synthesized with a model pegmatitic composition, one of which is highly enriched in Li (> 1 wt %, PEG2-blue) and the other one essentially Li-free (PEG2-Li-free). Diffusion couple experiments were performed to determine the chemical diffusivity of Li in dry pegmatitic melts. Experiments were conducted using rapid-heat and rapid-quench cold-seal pressure vessels in a temperature range of 650–940 ∘C at 100 MPa with Ar as the pressure medium. We observed rapidly formed diffusion profiles, driven by an interdiffusive exchange of the monovalent alkalis Li and Na, while the other elements are immobile on the timescale of experiments (1–30 min). From these experiments, activation energies for Li–Na interdiffusion were determined as 99 ± 7 kJ mol−1 with a pre-exponential factor of log D0 = −5.05 ± 0.33 (D0 in m2 s−1). Li and Na partitioning between the stronger depolymerized PEG2-blue and the less depolymerized PEG2-Li-free leads to a concentration jump at the interface; i.e. Na is enriched in the more depolymerized PEG2-blue. Li–Na interdiffusion coefficients in the studied melt composition are in a similar range as Li and Na tracer diffusivities in other dry aluminosilicate melts, confirming little to no effect of aluminosilicate melt composition on Li diffusivity. Thus, added fluxes do not enhance the Li diffusivity in the same way as observed for H2O (Holycross et al., 2018; Spallanzani et al., 2022). Using melt viscosity as a proxy for the polymerization of the melt shows that water has a stronger potential to depolymerize a melt compared to other fluxing elements. Faster diffusion of 6Li compared to 7Li leads to a strong Li isotope fractionation along the diffusion profile, resulting in δ7Li as low as −80 ‰ relative to the diffusion-unaffected regions. This diffusive isotope fractionation can be quantified with an empirical isotope fractionation factor (β) of 0.20 ± 0.04, similar to previously observed β values for Li diffusion in melts. This suggests in accordance with previously published data that a β value of ca. 0.2 seems to be universally applicable to diffusive Li isotope fractionation in aluminosilicate melts

Point-Contact Conductances from Density Correlations

We formulate and prove an exact relation which expresses the moments of the two-point conductance for an open disordered electron system in terms of certain density correlators of the corresponding closed system. As an application of the relation, we demonstrate that the typical two-point conductance for the Chalker-Coddington model at criticality transforms like a two-point function in conformal field theory.Comment: 4 pages, 2 figure