Recovery of the X-Ray Transient QX Nor (=X1608-52) in Outburst and Quiescence

We present optical and near-IR observations of QX Nor, the counterpart to the recurrent soft X-ray transient X1608-52, after its reappearance following the X-ray outburst in February 1996. The object has been seen only once before, during an X-ray outburst in 1977. Data from 3-5 months after the outburst show the counterpart at a mean magnitude of R=20.2 and variable on timescales of days. A comparison with identical observations in 1995 implies that the object has brightened by at least 1.8 mag in R following the X-ray outburst. We also detected QX Nor in the IR in both quiescence and outburst. A faint source is visible in the J but not the R band in May 1995. These first observations in the quiescent state yield magnitudes and colors consistent with optical emission from a low mass companion in the binary system, as is true in other soft X-ray transients.Comment: 10 pages including 4 figures and 2 tables; Uses AASTeX 4.0; Accepted for publication in The Astrophysical Journal, Volume 485, August 20, 199

Relativistic precession around rotating neutron stars: Effects due to frame-dragging and stellar oblateness

General relativity predicts that a rotating body produces a frame-dragging (or Lense-Thirring) effect: the orbital plane of a test particle in a non-equatorial orbit precesses about the body's symmetry axis. In this paper we compute the precession frequencies of circular orbits around rapidly rotating neutron stars for a variety of masses and equations of state. The precession frequencies computed are expressed as numerical functions of the orbital frequency observed at infinity. The post-Newtonian expansion of the exact precession formula is examined to identify the relative magnitudes of the precession caused by the Lense-Thirring effect, the usual Newtonian quadrupole effect and relativistic corrections. The first post-Newtonian correction to the Newtonian quadrupole precession is derived in the limit of slow rotation. We show that the post-Newtonian precession formula is a good approximation to the exact precession close to the neutron star in the slow rotation limit (up to \sim 400 Hz in the present context). The results are applied to recent RXTE observations of neutron star low-mass X-ray binaries, which display kHz quasi-periodic oscillations and, within the framework of beat frequency models, allow the measurement of both the neutron star spin frequency and the Keplerian frequency of the innermost ring of matter in the accretion disk around it. For a wide range of realistic equations of state, we find that the predicted precession frequency of this ring is close to one half of the low-frequency (\sim 20 - 35 Hz) quasi-periodic oscillations seen in several Atoll sources.Comment: 35 pages including 10 figures and 6 tables. To appear in the Astrophysical Journa

New Results for Two Optically Faint Low Mass X-Ray Binary Systems

We present optical photometry of the low mass X-ray binary systems GX 349+2 and Ser X-1. Extensive VRI photometry of the faint optical counterpart (V=18.4) to GX 349+2 reveals a period of 22.5 +/- 0.1 h and half-amplitude 0.2 mag. This result confirms and extends our previously reported 22 h period. No color change is detected over the orbit, although the limits are modest. We also report the discovery of two new variable stars in the field of GX 349+2, including a probable W UMa system. Ser X-1 is one of the most intense persistent X-ray burst sources known. It is also one of only three burst systems for which simultaneous optical and X-ray bursts have been observed. The faint blue optical counterpart MM Ser (B~19.2) has long been known to have a companion 2.1" distant. Our images indicate that MM Ser is itself a further superposition of two stars, separated by only 1". At the very least, the ratio of inferred burst to quiescent optical flux is affected by the discovery of this additional component. In the worst case, the wrong object may have previously been assumed as the optical counterpart.Comment: 16 pages including 10 figures and 3 tables; Uses AASTeX 4.0; Accepted for publication in The Astrophysical Journal, Volume 490, November 20, 199

The Formation of Low-Mass Transient X-Ray Binaries

We consider constraints on the formation of low-mass X-ray binaries containing neutron stars (NLMXBs) arising from the presence of soft X-ray transients among these systems. We show that in short-period systems driven by angular momentum loss these constraints require the secondary at the beginning of mass transfer to have a mass > 1.2 M_sun, and to be significantly nuclear-evolved. As a consequence a comparatively large fraction of such systems appear as soft X-ray transients even at short periods, as observed. Moreover the large initial secondary masses account for the rarity of NLMXBs at periods less than 3 hr. In contrast, NLMXB populations forming with large kick velocities would not have these properties, suggesting that the kick velocity is generally small compared to the pre-SN orbital velocity in a large fraction of systems. We derive constraints on progenitor system parameters and on the strength of magnetic braking.Comment: Accepted for publication in ApJ, 19 pages, 4 figure

Hydrophilic interaction liquid chromatography (HILIC) in proteomics

In proteomics, nanoflow multidimensional chromatography is now the gold standard for the separation of complex mixtures of peptides as generated by in-solution digestion of whole-cell lysates. Ideally, the different stationary phases used in multidimensional chromatography should provide orthogonal separation characteristics. For this reason, the combination of strong cation exchange chromatography (SCX) and reversed-phase (RP) chromatography is the most widely used combination for the separation of peptides. Here, we review the potential of hydrophilic interaction liquid chromatography (HILIC) as a separation tool in the multidimensional separation of peptides in proteomics applications. Recent work has revealed that HILIC may provide an excellent alternative to SCX, possessing several advantages in the area of separation power and targeted analysis of protein post-translational modifications

Perturbation of the yeast N-acetyltransferase NatB induces elevation of protein phosphorylation levels

<p>Abstract</p> <p>Background</p> <p>The addition of an acetyl group to protein N-termini is a widespread co-translational modification. NatB is one of the main N-acetyltransferases that targets a subset of proteins possessing an N-terminal methionine, but so far only a handful of substrates have been reported. Using a yeast <it>nat3Δ </it>strain, deficient for the catalytic subunit of NatB, we employed a quantitative proteomics strategy to identify NatB substrates and to characterize downstream effects in <it>nat3Δ</it>.</p> <p>Results</p> <p>Comparing by proteomics WT and <it>nat3Δ </it>strains, using metabolic ¹⁵N isotope labeling, we confidently identified 59 NatB substrates, out of a total of 756 detected acetylated protein N-termini. We acquired in-depth proteome wide measurements of expression levels of about 2580 proteins. Most remarkably, NatB deletion led to a very significant change in protein phosphorylation.</p> <p>Conclusions</p> <p>Protein expression levels change only marginally in between WT and <it>nat3Δ</it>. A comparison of the detected NatB substrates with their orthologous revealed remarkably little conservation throughout the phylogenetic tree. We further present evidence of post-translational N-acetylation on protein variants at non-annotated N-termini. Moreover, analysis of downstream effects in <it>nat3Δ </it>revealed elevated protein phosphorylation levels whereby the kinase Snf1p is likely a key element in this process.</p

Enhancing Europe’s global power: a scenario exercise with eight proposals

In the present context of intensifying competition between the major trading economies and potentially game-changing technological developments, the European Union is generally seen as the weaker party. Lacking the ‘hard power’ derived from military capabilities, it has laid claim to a ‘soft power’ of normative influence externally, yet even that is only partially utilised. Nor has Europe been able to exercise the power to coerce – ‘sharp power’ – commensurate with its economic weight as a trading bloc equivalent in size and reach to the US or China, its most prominent global competitors. How can Europe strengthen its position, and in what fields? Through a scenario exercise, we develop eight policy proposals aimed at countering Europe´s vulnerabilities and enabling it to assert its sharp and soft power more effectively. Specifically, we consider the feasibility, means and scope for their realisation. Together, they provide a transformative agenda for the EU’s position in the world

The Leukemia-Associated Mllt10/Af10-Dot1l Are Tcf4/β-Catenin Coactivators Essential for Intestinal Homeostasis

The leukemia-associated Mllt10/Af10 and its partner the histone methyltransferase Dot1l are identified as Tcf4/β-catenin co-activators and shown to be essential for Wnt-driven endogenous gene expression, intestinal development and homeostasis

Dimer interface of Bovine cytochrome c oxidase is influenced by local posttranslational modifications and lipid binding

Bovine cytochrome c oxidase is an integral membrane protein complex comprising 13 protein subunits and associated lipids. Dimerization of the complex has been proposed; however, definitive evidence for the dimer is lacking. We used advanced mass spectrometry methods to investigate the oligomeric state of cytochrome c oxidase and the potential role of lipids and posttranslational modifications in its subunit interfaces. Mass spectrometry of the intact protein complex revealed that both the monomer and the dimer are stabilized by large lipid entities. We identified these lipid species from the purified protein complex, thus implying that they interact specifically with the enzyme. We further identified phosphorylation and acetylation sites of cytochrome c oxidase, located in the peripheral subunits and in the dimer interface, respectively. Comparing our phosphorylation and acetylation sites with those found in previous studies of bovine, mouse, rat, and human cytochrome c oxidase, we found that whereas some acetylation sites within the dimer interface are conserved, suggesting a role for regulation and stabilization of the dimer, phosphorylation sites were less conserved and more transient. Our results therefore provide insights into the locations and interactions of lipids with acetylated residues within the dimer interface of this enzyme, and thereby contribute to a better understanding of its structure in the natural membrane. Moreover dimeric cytochrome c oxidase, comprising 20 transmembrane, six extramembrane subunits, and associated lipids, represents the largest integral membrane protein complex that has been transferred via electrospray intact into the gas phase of a mass spectrometer, representing a significant technological advance

Unambiguous phosphosite localization using electron-transfer/higher-energy collision dissociation (EThcD).

We recently introduced a novel scheme combining electron-transfer and higher-energy collision dissociation (termed EThcD), for improved peptide ion fragmentation and identification. We reasoned that phosphosite localization, one of the major hurdles in high-throughput phosphoproteomics, could also highly benefit from the generation of such EThcD spectra. Here, we systematically assessed the impact on phosphosite localization utilizing EThcD in comparison to methods employing either ETD or HCD, respectively, using a defined synthetic phosphopeptide mixture and also using a larger data set of Ti(4+)-IMAC enriched phosphopeptides from a tryptic human cell line digest. In combination with a modified version of phosphoRS, we observed that in the majority of cases EThcD generated richer and more confidently identified spectra, resulting in superior phosphosite localization scores. Our data demonstrates the distinctive potential of EThcD for PTM localization, also beyond protein phosphorylation