LST8 negatively regulates amino acid biosynthesis as a component of the TOR pathway

LST8, a Saccharomyces cerevisiae gene encoding a 34-kD WD-repeat protein, was identified by mutations that caused defects in sorting Gap1p to the plasma membrane. Here, we report that the Gap1p sorting defect in the lst8-1 mutant results from derepression of Rtg1/3p activity and the subsequent accumulation of high levels of intracellular amino acids, which signal Gap1p sorting to the vacuole. To identify the essential function of Lst8p, we isolated lst8 mutants that are temperature-sensitive for growth. These mutants show hypersensitivity to rapamycin and derepressed Gln3p activity like cells with compromised TOR pathway activity. Like tor2 mutants, lst8 mutants also have cell wall integrity defects. Confirming a role for Lst8p in the TOR pathway, we find that Lst8p associates with both Tor1p and Tor2p and is a peripheral membrane protein that localizes to endosomal or Golgi membranes and cofractionates with Tor1p. Further, we show that a sublethal concentration of rapamycin mimics the Gap1p sorting defect of an lst8 mutant. Finally, the different effects of lst8 alleles on the activation of either the Rtg1/3p or Gln3p transcription factors reveal that these two pathways constitute distinct, genetically separable outputs of the Tor–Lst8 regulatory complex

Redox signaling via the molecular chaperone BiP protects cells against endoplasmic reticulum-derived oxidative stress

Oxidative protein folding in the endoplasmic reticulum (ER) has emerged as a potentially significant source of cellular reactive oxygen species (ROS). Recent studies suggest that levels of ROS generated as a byproduct of oxidative folding rival those produced by mitochondrial respiration. Mechanisms that protect cells against oxidant accumulation within the ER have begun to be elucidated yet many questions still remain regarding how cells prevent oxidant-induced damage from ER folding events. Here we report a new role for a central well-characterized player in ER homeostasis as a direct sensor of ER redox imbalance. Specifically we show that a conserved cysteine in the lumenal chaperone BiP is susceptible to oxidation by peroxide, and we demonstrate that oxidation of this conserved cysteine disrupts BiP's ATPase cycle. We propose that alteration of BiP activity upon oxidation helps cells cope with disruption to oxidative folding within the ER during oxidative stress.Cornell UniversityNational Institutes of Health (U.S.) (Grant GM46941

The Flux Auto- and Cross-Correlation of the Lyman-alpha Forest. II. Modelling Anisotropies with Cosmological Hydrodynamic Simulations

The isotropy of the Lyman-alpha forest in real-space uniquely provides a measurement of cosmic geometry at z > 2. The angular diameter distance for which the correlation function along the line of sight and in the transverse direction agree corresponds to the correct cosmological model. However, the Lyman-alpha forest is observed in redshift-space where distortions due to Hubble expansion, bulk flows, and thermal broadening introduce anisotropy. Similarly, a spectrograph's line spread function affects the autocorrelation and cross-correlation differently. In this the second paper of a series on using the Lyman-alpha forest observed in pairs of QSOs for a new application of the Alcock-Paczynski (AP) test, these anisotropies and related sources of potential systematic error are investigated with cosmological hydrodynamic simulations. Three prescriptions for galactic outflow were compared and found to have only a marginal effect on the Lyman-alpha flux correlation (which changed by at most 7% with use of the currently favored variable-momentum wind model vs. no winds at all). An approximate solution for obtaining the zero-lag cross-correlation corresponding to arbitrary spectral resolution directly from the zero-lag cross-correlation computed at full-resolution (good to within 2% at the scales of interest) is presented. Uncertainty in the observationally determined mean flux decrement of the Lyman-alpha forest was found to be the dominant source of systematic error; however, this is reduced significantly when considering correlation ratios. We describe a simple scheme for implementing our results, while mitigating systematic errors, in the context of a future application of the AP test.Comment: 20 page

Probing dark energy using baryonic oscillations in the galaxy power spectrum as a cosmological ruler

We show that the baryonic oscillations expected in the galaxy power spectrum may be used as a "standard cosmological ruler'' to facilitate accurate measurement of the cosmological equation of state. Our approach involves a straight-forward measurement of the oscillation "wavelength'' in Fourier space, which is fixed by fundamental linear physics in the early Universe and hence is highly model-independent. We quantify the ability of future large-scale galaxy redshift surveys with mean redshifts z~1 and z~3 to delineate the baryonic peaks in the power spectrum, and derive corresponding constraints on the parameter w describing the equation of state of the dark energy. For example, a survey of three times the Sloan volume at z ~ 1 can produce a measurement with accuracy dw ~ 0.1. We suggest that this method of measuring the dark energy powerfully complements other probes such as Type Ia supernovae, and suffers from a different (and arguably less serious) set of systematic uncertainties.Comment: Submitted to Astrophysical Journal, 11 pages, 8 figure

Beyond the plane-parallel and Newtonian approach: Wide-angle redshift distortions and convergence in general relativity

We extend previous analyses of wide-angle correlations in the galaxy power spectrum in redshift space to include all general relativistic effects. These general relativistic corrections to the standard approach become important on large scales and at high redshifts, and they lead to new terms in the wide-angle correlations. We show that in principle the new terms can produce corrections of nearly 10 % on Gpc scales over the usual Newtonian approximation. General relativistic corrections will be important for future large-volume surveys such as SKA and Euclid, although the problem of cosmic variance will present a challenge in observing this.Comment: 14 pages, 5 figures; Typo in equation 5 corrected; results unaffecte

The X-ray Luminosity Function of Nearby Rich and Poor Clusters of Galaxies: A Cosmological Probe

In this letter, we present a new determination of the local (z<0.09) X-ray luminosity function (XLF) using a large, statistical sample of 294 Abell clusters and the ROSAT All-Sky-Survey. Given our large sample size, we have reduced errors by a factor of two for L(X)(0.5-2keV)>10^43 ergs/sec. We combine our data with previous work in order to explore possible constraints imposed by the shape of the XLF on cosmological models. A set of currently viable cosmologies is used to construct theoretical XLFs assuming Lx is proportional to M^p and a sigma_8-Omega_0 constraint (from Viana & Liddle 1996) based on the local X-ray temperature function. We fit these models to our observed XLF and verify that the simplest adiabatic, analytic scaling relation (e.g. Kaiser 1986) disagrees strongly with observations. If we assume that clusters can be described by the pre-heated, constant core-entropy models of Evrard & Henry (1991) then the observed XLF is consistent only with 0.1 < Omega_0 < 0.4 if the energy per unit mass in galaxies is roughly equal to the gas energy (ie if beta=1). (abridged)Comment: 4 pages, 2 figures, accepted for publication in ApJ Letters. uses emulateapj.st

Deep Imaging of AXJ2019+112: The Luminosity of a ``Dark Cluster''

We detect a distant cluster of galaxies centered on the QSO lens and luminous X-ray source AXJ2019+112, a.k.a. ``The Dark Cluster'' (Hattori et al 1997). Using deep V,I Keck images and wide-field K_s imaging from the NTT, a tight red sequence of galaxies is identified within a radius of 0.2 h^{-1} Mpc of the known z=1.01 elliptical lensing galaxy. The sequence, which includes the central elliptical galaxy, has a slope in good agreement with the model predictions of Kodama et al (1998) for z~1. We estimate the integrated rest-frame luminosity of the cluster to be L_V > 3.2 x 10^{11}h^{-2}L_{\sun} (after accounting for significant extinction at the low latitude of this field), more than an order of magnitude higher than previous estimates. The central region of the cluster is deconvolved using the technique of Magain, Courbin & Sohy (1998), revealing a thick central arc coincident with an extended radio source. All the observed lensing features are readily explained by differential magnification of a radio loud AGN by a shallow elliptical potential. The QSO must lie just outside the diamond caustic, producing two images, and the arc is a highly magnified image formed from a region close to the center of the host galaxy, projecting inside the caustic. The mass--to--light ratio within an aperture of 0.4 h ^{-1} Mpc is M_x/L_V= 224^{+112}_{-78}h(M/L_V)_{\sun}, using the X-ray temperature. The strong lens model yields a compatible value, M/L_V= 372^{+94}_{-94}h(M/L_V)_{\sun}, whereas an independent weak lensing analysis sets an upper limit of M/L_V <520 h(M/L_V)_{\sun}, typical of massive clusters.Comment: AAS Latex format, 24 pages, 9 figures. Fig 1a,b available at http://astro.berkeley.edu/~benitezn/cluster.html . Submitted to ApJ on August 15t

The Hubble Deep Field South Flanking Fields

As part of the Hubble Deep Field South program, a set of shorter 2-orbit observations were obtained of the area adjacent to the deep fields. The WFPC2 flanking fields cover a contiguous solid angle of 48 square arcminutes. Parallel observations with the STIS and NICMOS instruments produce a patchwork of additional fields with optical and near-infrared (1.6 micron) response. Deeper parallel exposures with WFPC2 and NICMOS were obtained when STIS observed the NICMOS deep field. These deeper fields are offset from the rest, and an extended low surface brightness object is visible in the deeper WFPC2 flanking field. In this data paper, which serves as an archival record of the project, we discuss the observations and data reduction, and present SExtractor source catalogs and number counts derived from the data. Number counts are broadly consistent with previous surveys from both ground and space. Among other things, these flanking field observations are useful for defining slit masks for spectroscopic follow-up over a wider area around the deep fields, for studying large-scale structure that extends beyond the deep fields, for future supernova searches, and for number counts and morphological studies, but their ultimate utility will be defined by the astronomical community.Comment: 46 pages, 15 figures. Images and full catalogs available via the HDF-S at http://www.stsci.edu/ftp/science/hdfsouth/hdfs.html at present. The paper is accepted for the February 2003 Astronomical Journal. Full versions of the catalogs will also be available on-line from AJ after publicatio