Metal binding to the Polaris protein associated with ethylene sensing by plants

Copper ions are essential to life, but toxic if not tightly regulated. In the model organism Arabidopsis thaliana, the ER-localised ethylene receptor, ETR1, requires Cu(I) at an intramembrane site, dependent on the Cu(I)-transporting P-type ATPase RAN1. However, the detailed biochemical mechanisms of Cu(I)-delivery, and ethylene binding, are unknown. The protein Polaris (PLS), a negative regulator of ethylene signalling, shares some characteristics of known Cu(I)-metallochaperones, and was proposed to be involved in correct Cu(I)-metalation of ETR1. Here, metal binding to PLS has been investigated in-vitro, allowing prediction of its likely metalation state in-vivo. PLS bound Cu(I) and Zn(II) in 2:1 protein:metal stoichiometries, with β2 affinities of 3.79 x1019 and 3.76 x1012 M-2 respectively. Recently developed metalation calculators, based on metal-availability read-out from calibrated bacterial cells, were adapted to use these constants. The metal affinities of the Arabidopsis cytosolic Cu(I) chaperone Atx1, showed Cu(I) bound in a 1:1 and Zn(II) a 2:1 stoichiometry, and its metalation was modelled. This work showed, in E. coli BL21(DE3), by reading out CueR-dependent copA transcripts, Atx1 overexpression decreased Cu(I)-availability, when calibrated using E. coli JM109, with implications for heterologous expression of metalloproteins in bacteria. Availabilities, measured here, were used to correctly predict the metal preference of Atx1 in E. coli, when tested post-extraction. Using the Atx1 Cu(I)-affinity of 5.47 x10-18 M as an estimate for the intracellular buffered Cu(I)-availability in the cytosol of Arabidopsis, the metalation of PLS as a function of Atx1 Cu(I)-metalation showed it was unlikely PLS extracts Cu(I) directly from the buffer, at least not as a 2:1 complex. This thesis speculates upon the putative roles of PLS in the biochemical activities of ETR1, and considers some of the implications and challenges associated with the potential formation of metal-dependent 2:1 ligand:metal complexes (with analogy to PLS2:Cu(I)) in biological systems, more broadly

Amplification of simian retroviral sequences from human recipients of baboon liver transplants

Investigations into the use of baboons as organ donors for human transplant recipients, a procedure called xenotransplantation, have raised the specter of transmitting baboon viruses to humans and possibly establishing new human infectious diseases. Retrospective analysis of tissues from two human transplant recipients with end-stage hepatic disease who died 70 and 27 days after the transplantation of baboon livers revealed the presence of two simian retroviruses of baboon origin, simian foamy virus (SFV) and baboon endogenous virus (BaEV), in multiple tissue compartments. The presence of baboon mitochondrial DNA was also detected in these same tissues, suggesting that xenogeneic 'passenger leukocytes' harboring latent or active viral infections had migrated from the xenografts to distant sites within the human recipients. The persistence of SFV and BaEV in human recipients throughout the posttransplant period underscores the potential infectious risks associated with xenotransplantation

Localized precipitation and runoff on Mars

We use the Mars Regional Atmospheric Modeling System (MRAMS) to simulate lake storms on Mars, finding that intense localized precipitation will occur for lake size >=10^3 km^2. Mars has a low-density atmosphere, so deep convection can be triggered by small amounts of latent heat release. In our reference simulation, the buoyant plume lifts vapor above condensation level, forming a 20km-high optically-thick cloud. Ice grains grow to 200 microns radius and fall near (or in) the lake at mean rates up to 1.5 mm/hr water equivalent (maximum rates up to 6 mm/hr water equivalent). Because atmospheric temperatures outside the surface layer are always well below 273K, supersaturation and condensation begin at low altitudes above lakes on Mars. In contrast to Earth lake-effect storms, lake storms on Mars involve continuous precipitation, and their vertical velocities and plume heights exceed those of tropical thunderstorms on Earth. Convection does not reach above the planetary boundary layer for lakes O(10^2) mbar. Instead, vapor is advected downwind with little cloud formation. Precipitation occurs as snow, and the daytime radiative forcing at the land surface due to plume vapor and storm clouds is too small to melt snow directly (<+10 W/m^2). However, if orbital conditions are favorable, then the snow may be seasonally unstable to melting and produce runoff to form channels. We calculate the probability of melting by running thermal models over all possible orbital conditions and weighting their outcomes by probabilities given by Laskar et al., 2004. We determine that for an equatorial vapor source, sunlight 15% fainter than at present, and snowpack with albedo 0.28 (0.35), melting may occur with 4%(0.1%) probability. This rises to 56%(12%) if the ancient greenhouse effect was modestly (6K) greater than today.Comment: Submitted to JGR Planet

Geophysical Surveys Across the Boise Hydrogeophysical Research Site to Determine Geophysical Parameters of a Shallow, Alluvial Aquifer

At the Boise Hydrogeophysical Research Site (BHRS), we are characterizing the hydrogeophysical parameters of a cobble-and-sand, unconfined aquifer using a wide variety of geophysical methods. Our goal is to develop methods for mapping variations in permeability by combining non-invasive geophysical data with hydrologic measurements. We are using seismic, ground penetrating radar, and electrical methods in a variety of configurations to provide images of and parameter distributions at the BHRS. Issues such as resolution, depth of penetration, and the ability to image the desired parameters will help determine the most effective methods. Supporting data sets from the BHRS include core analyses and geophysical logs from 18 wells at the site. We will use these data to verify our geophysical interpretations. The various geophysical methods and acquisition geometries, combined with the well control, will provide an outstanding data set to characterize the heterogeneity of the subsurface beneath this alluvial aquifer, and find ways to map permeability with geophysical information

Manacled to Identity: Cosmopolitanism, Class, and ‘The Culture Concept’ in Stephen Crane

This article begins with a close reading of Stephen Crane’s short story ‘Manacled’ from 1900, which situates this rarely considered short work within the context of contemporary debates about realism. I then proceed to argue that many of the debates raised by the tale have an afterlife in our own era of American literary studies, which has frequently focused on questions of ‘identity’ and ‘culture’ in its reading of realism and naturalism to the exclusion of the importance of cosmopolitan discourses of diffusion and exchange across national borders. I then offer a brief reading of Crane’s novel George’s Mother, which follows Walter Benn Michaels in suggesting that the recent critical attention paid to particularities of cultural difference in American studies have come to conflate ideas of class and social position with ideas of culture in ways that have ultimately obscured the presence of genuine historical inequalities in US society. In order to challenge this critical commonplace, I situate Crane’s work within a history of transatlantic cosmopolitanism associated with the ideas of Franz Boas and Matthew Arnold to demonstrate the ways in which Crane’s narratives sought out an experience of the universal within their treatments of the particular