4,935 research outputs found
Conformational changes in the GTPase modules of the signal reception particle and its receptor drive initiation of protein translocation
During cotranslational protein targeting, two guanosine triphosphatase (GTPase) in the signal recognition particle (SRP) and its receptor (SR) form a unique complex in which hydrolyses of both guanosine triphosphates (GTP) are activated in a shared active site. It was thought that GTP hydrolysis drives the recycling of SRP and SR, but is not crucial for protein targeting. Here, we examined the translocation efficiency of mutant GTPases that block the interaction between SRP and SR at specific stages. Surprisingly, mutants that allow SRP–SR complex assembly but block GTPase activation severely compromise protein translocation. These mutations map to the highly conserved insertion box domain loops that rearrange upon complex formation to form multiple catalytic interactions with the two GTPs. Thus, although GTP hydrolysis is not required, the molecular rearrangements that lead to GTPase activation are essential for protein targeting. Most importantly, our results show that an elaborate rearrangement within the SRP–SR GTPase complex is required to drive the unloading and initiate translocation of cargo proteins
Testing for Multiple Bubbles 1: Historical Episodes of Exuberance and Collapse in the S&P 500
Published in International Economic Review, https://doi.org/10.1111/iere.12132</p
Testing for Multiple Bubbles 2: Limit Theory of Real Time Detectors
Singapore MOE Academic Research Tier 2Published in International Economic Review, https://doi.org/10.1111/iere.12131</p
Testing for Multiple Bubbles
Identifying and dating explosive bubbles when there is periodically collapsing behavior over time has been a major concern in the economics literature and is of great importance for practitioners. The complexity of the nonlinear structure inherent in multiple bubble phenomena within the same sample period makes econometric analysis particularly difficult. The present paper develops new recursive procedures for practical implementation and surveillance strategies that may be employed by central banks and fiscal regulators. We show how the testing procedure and dating algorithm of Phillips, Wu and Yu (2011, PWY) are affected by multiple bubbles and may fail to be consistent. The present paper proposes a generalized version of the sup ADF test of PWY to address this difficulty, derives its asymptotic distribution, introduces a new date-stamping strategy for the origination and termination of multiple bubbles, and proves consistency of this dating procedure. Simulations show that the test significantly improves discriminatory power and leads to distinct power gains when multiple bubbles occur. Empirical applications are conducted to S&P 500 stock market data over a long historical period from January 1871 to December 2010. The new approach identifies many key historical episodes of exuberance and collapse over this period, whereas the strategy of PWY and the CUSUM procedure locate far fewer episodes in the same sample range.Date-stamping strategy, Generalized sup ADF test, Multiple bubbles, Rational bubble, Periodically collapsing bubbles, Sup ADF test
Specification Sensitivity in Right-Tailed Unit Root Testing for Explosive Behavior
Right-tailed unit root tests have proved promising for detecting exuberance in economic and financial activities. Like left-tailed tests, the limit theory and test performance are sensitive to the null hypothesis and the model specification used in parameter estimation. This paper aims to provide some empirical guidelines for the practical implementation of right-tailed unit root tests, focussing on the sup ADF test of Phillips, Wu and Yu (2011), which implements a right-tailed ADF test repeatedly on a sequence of forward sample recursions. We analyze and compare the limit theory of the sup ADF test under different hypotheses and model specifications. The size and power properties of the test under various scenarios are examined in simulations and some recommendations for empirical practice are given. Empirical applications to the Nasdaq and to Australian and New Zealand housing data illustrate these specification issues and reveal their practical importance in testing.Unit root test, Mildly explosive process, Recursive regression, Size and power
Bounds on the spectral shift function and the density of states
We study spectra of Schr\"odinger operators on \RR^d. First we consider a
pair of operators which differ by a compactly supported potential, as well as
the corresponding semigroups. We prove almost exponential decay of the singular
values of the difference of the semigroups as and deduce
bounds on the spectral shift function of the pair of operators.
Thereafter we consider alloy type random Schr\"odinger operators. The single
site potential is assumed to be non-negative and of compact support. The
distributions of the random coupling constants are assumed to be H\"older
continuous. Based on the estimates for the spectral shift function, we prove a
Wegner estimate which implies H\"older continuity of the integrated density of
states.Comment: Latex 2e, 15 page
Concerted Complex Assembly and GTPase Activation in the Chloroplast Signal Recognition Particle
The universally conserved signal recognition particle (SRP) and SRP receptor (SR) mediate the cotranslational targeting of proteins to cellular membranes. In contrast, a unique chloroplast SRP in green plants is primarily dedicated to the post-translational targeting of light harvesting chlorophyll a/b binding (LHC) proteins. In both pathways, dimerization and activation between the SRP and SR GTPases mediate the delivery of cargo; whether and how the GTPase cycle in each system adapts to its distinct substrate proteins were unclear. Here, we show that interactions at the active site essential for GTPase activation in the chloroplast SRP and SR play key roles in the assembly of the GTPase complex. In contrast to their cytosolic homologues, GTPase activation in the chloroplast SRP–SR complex contributes marginally to the targeting of LHC proteins. These results demonstrate that complex assembly and GTPase activation are highly coupled in the chloroplast SRP and SR and suggest that the chloroplast GTPases may forego the GTPase activation step as a key regulatory point. These features may reflect adaptations of the chloroplast SRP to the delivery of their unique substrate protein
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