Structural determinants for NF-Y/DNA interaction at the CCAAT box

The recently determined crystal structures of the sequence-specific transcription factor NF-Y have illuminated the structural mechanism underlying transcription at the CCAAT box. NF-Y is a trimeric protein complex composed by the NF-YA, NF-YB, and NF-YC subunits. NF-YB and NF-YC contain a histone-like domain and assemble on a head-to-tail fashion to form a dimer, which provides the structural scaffold for the DNA sugar-phosphate backbone binding (mimicking the nucleosome H2A/H2B\ue2\u80\u93DNA assembly) and for the interaction with NF-YA. The NF-YA subunit hosts two structurally extended \uce\ub1-helices; one is involved in NF-YB/NF-YC binding and the other inserts deeply into the DNA minor groove, providing exquisite sequence-specificity for recognition and binding of the CCAAT box. The analysis of these structural data is expected to serve as a powerful guide for future experiments aimed at understanding the role of post-translational modification at NF-Y regulation sites and to unravel the three-dimensional architecture of higher order complexes formed between NF-Y and other transcription factors that act synergistically for transcription activation. Moreover, these structures represent an excellent starting point to challenge the formation of a stable hybrid nucleosome between NF-Y and core histone proteins, and to rationalize the fine molecular details associated with the wide combinatorial association of plant NF-Y subunits

On a microcanonical relation between continuous and discrete spin models

A relation between a class of stationary points of the energy landscape of continuous spin models on a lattice and the configurations of a Ising model defined on the same lattice suggests an approximate expression for the microcanonical density of states. Based on this approximation we conjecture that if a O(n) model with ferromagnetic interactions on a lattice has a phase transition, its critical energy density is equal to that of the n = 1 case, i.e., a system of Ising spins with the same interactions. The conjecture holds true in the case of long-range interactions. For nearest-neighbor interactions, numerical results are consistent with the conjecture for n=2 and n=3 in three dimensions. For n=2 in two dimensions (XY model) the conjecture yields a prediction for the critical energy of the Berezinskij-Kosterlitz-Thouless transition, which would be equal to that of the two-dimensional Ising model. We discuss available numerical data in this respect.Comment: 5 pages, no figure

Less safety for more efficiency: Water relations and hydraulics of the invasive tree Ailanthus altissima (Mill.) Swingle compared with native Fraxinus ornus L

Invasion of natural habitats by alien trees is a threat to forest conservation. Our understanding of fundamental ecophysiological mechanisms promoting plant invasions is still limited, and hydraulic and water relation traits have been only seldom included in studies comparing native and invasive trees. We compared several leaf and wood functional and mechanistic traits in co-occurring Ailanthus altissima (Mill.) Swingle (Aa) and Fraxinus ornus L. (Fo). Aa is one of the most invasive woody species in Europe and North America, currently outcompeting several native trees including Fo. We aimed at quantifying inter-specific differences in terms of: (i) performance in resource use and acquisition; (ii) hydraulic efficiency and safety; (iii) carbon costs associated to leaf and wood construction; and (iv) plasticity of functional and mechanistic traits in response to light availability. Traits related to leaf and wood construction and drought resistance significantly differed between the two species. Fo sustained higher structural costs than Aa, but was more resistant to drought. The lower resistance to drought stress of Aa was counterbalanced by higher water transport efficiency, but possibly required mechanisms of resilience to drought-induced hydraulic damage. Larger phenotypic plasticity of Aa in response to light availability could also promote the invasive potential of the species

Magnetic Fields at First Order Phase Transition: A Threat to Electroweak Baryogenesis

The generation of the observed baryon asymmetry may have taken place during the electroweak phase transition, thus involving physics testable at LHC, a scenario dubbed electroweak baryogenesis. In this paper we point out that the magnetic field which is produced in the bubbles of a first order phase transition endangers the baryon asymmetry produced in the bubble walls. The reason being that the produced magnetic field couples to the sphaleron magnetic moment and lowers the sphaleron energy; this strengthens the sphaleron transitions inside the bubbles and triggers a more effective wash out of the baryon asymmetry. We apply this scenario to the Minimal Supersymmetric extension of the Standard Model (MSSM) where, in the absence of a magnetic field, successful electroweak baryogenesis requires the lightest CP-even Higgs and the right-handed stop masses to be lighter than about 127 GeV and 120 GeV, respectively. We show that even for moderate values of the magnetic field, the Higgs mass required to preserve the baryon asymmetry is below the present experimental bound. As a consequence electroweak baryogenesis within the MSSM should be confronted on the one hand to future measurements at the LHC on the Higgs and the right-handed stop masses, and on the other hand to more precise calculations of the magnetic field produced at the electroweak phase transition.Comment: 16 pages, 4 figures. Minor corrections and references added to match published versio

Forced expiratory volume in one second: A novel predictor of work disability in subjects with suspected obstructive sleep apnea

Whether the association of work disability with obstructive sleep apnea (OSA) is mainly due to the disease, i.e. the number and frequency of apneas-hypoapneas, or to coexisting factors independent from the disease, is not well-established. In this study, we aim to evaluate work ability in a group of subjects undergoing OSA workup and to identify the major contributors of impaired work ability. In a cross-sectional study, we enrolled 146 consecutive subjects who have been working for the last five years and referred to the sleep disorders outpatients’ clinic of the University-Hospital of Ferrara, Italy, with suspected OSA. After completing an interview in which the Work Ability Index (WAI) and the Epworth Sleepiness Scale (ESS) questionnaires were administered to assess work ability and excessive daytime sleepiness, respectively, subjects underwent overnight polysomnography for OSA diagnosing and spirometry. Of the 146 subjects, 140 (96%) completed the tests and questionnaires and, of these, 66 exhibited work disability (WAI < 37). OSA was diagnosed (apnea-hypopnea index 5) in 45 (68%) of the 66 subjects. After controlling for confounders, a lower level of forced expiratory volume at 1 second (FEV1), [odds ratio 0.97 (95% CI 0.95–1.00)], older age [1.09 (95% CI 1.03–1.15)], excessive daytime sleepiness [3.16 (95% CI 1.20–8.34)] and a worse quality of life [0.96 (95% CI 0.94–1.00)], but not OSA [1.04 (95% CI 0.41–2.62)], were associated with work disability. Patients with a higher number of diseases, in which OSA was not included, and a lower quality of life had an increased probability of absenteeism in the previous 12 months. In subjects with suspected OSA, FEV1 can be an important predictor of work disability

Canonical Expansion of PT-Symmetric Operators and Perturbation Theory

Let $H$ be any \PT symmetric Schr\"odinger operator of the type $-\hbar^2\Delta+(x_1^2+...+x_d^2)+igW(x_1,...,x_d)$ on $L^2(\R^d)$, where $W$ is any odd homogeneous polynomial and $g\in\R$. It is proved that $\P H$ is self-adjoint and that its eigenvalues coincide (up to a sign) with the singular values of $H$, i.e. the eigenvalues of $\sqrt{H^\ast H}$. Moreover we explicitly construct the canonical expansion of $H$ and determine the singular values $\mu_j$ of $H$ through the Borel summability of their divergent perturbation theory. The singular values yield estimates of the location of the eigenvalues \l_j of $H$ by Weyl's inequalities.Comment: 20 page

Stem photosynthesis contributes to non-structural carbohydrate pool and modulates xylem vulnerability to embolism in Fraxinus ornus L

Stem photosynthesis can significantly contribute to the carbon budget of woody plants, providing an extra carbon gain that might be crucial under drought stress causing leaf photosynthesis impairment and/or a reduced phloem transport.Stems of Fraxinus ornus L. saplings were covered with aluminum foil to test the impact of inhibition of stem photosynthesis on plant vulnerability to drought. Plants were water-stressed to target xylem water potential of-3.5 MPa and were then re-irrigated to field capacity to quantify their recovery capacity. Vulnerability to xylem embolism was assessed in light-exposed and stem-shaded saplings with both the hydraulic method and in vivo with X-ray phase contrast micro-computed tomography. We also measured non-structural carbohydrate (NSC) concentration and osmotic potential in bark and wood, separately.Stem shading increased xylem vulnerability to embolism formation under drought but did not influence the recovery phase. This difference was coupled with modification of the NSC pool and impaired osmoregulation, in particular in the wood of stem-shaded saplings compared to control ones.Our results indicate stem photosynthesis as an important source of local NSCs, directly or indirectly involved in osmoregulation processes, which could be crucial to enhance the hydraulic resistance to embolism formation and to endure drought

Afterglow rebrightenings as a signature of a long-lasting central engine activity? The emblematic case of GRB 100814A

In the past few years the number of well-sampled optical to NIR light curves of long Gamma-Ray Bursts (GRBs) has greatly increased particularly due to simultaneous multi-band imagers such as GROND. Combining these densely sampled ground-based data sets with the Swift UVOT and XRT space observations unveils a much more complex afterglow evolution than what was predicted by the most commonly invoked theoretical models. GRB 100814A represents a remarkable example of these interesting well-sampled events, showing a prominent late-time rebrightening in the optical to NIR bands and a complex spectral evolution. This represents a unique laboratory to test the different afterglow emission models. Here we study the nature of the complex afterglow emission of GRB 100814A in the framework of different theoretical models. Moreover, we compare the late-time chromatic rebrightening with those observed in other well-sampled long GRBs. We analysed the optical and NIR observations obtained with the seven-channel Gamma-Ray burst Optical and Near-infrared Detector at the 2.2 m MPG/ESO telescope together with the X-ray and UV data detected by the instruments onboard the Swift observatory. The broad-band afterglow evolution, achieved by constructing multi-instrument light curves and spectral energy distributions, will be discussed in the framework of different theoretical models. We find that the standard models that describe the broad-band afterglow emission within the external shock scenario fail to describe the complex evolution of GRB 100814A, and therefore more complex scenarios must be invoked. [abridged]Comment: 11 pages, 7 figures, 2 tables; Astronomy & Astrophysics, in pres

Complicated variations of early optical afterglow of GRB 090726

We report on a detection of an early rising phase of optical afterglow (OA) of a long GRB 090726. We resolve a complicated profile of the optical light curve. We also investigate the relation of the optical and X-ray emission of this event. We make use of the optical photometry of this OA obtained by the 0.5 m telescope of AI AS CR, supplemented by the data obtained by other observers, and the X-ray Swift/XRT data. The optical emission peaked at ~ 17.5 mag (R) at t-T0 ~ 500 s. We find a complex profile of the light curve during the early phase of this OA: an approximately power-law rise, a rapid transition to a plateau, a weak flare superimposed on the center of this plateau, and a slowly steepening early decline followed by a power-law decay. We discuss several possibilities to explain the short flare on the flat top of the optical light curve at t-T0 ~ 500 s; activity of the central engine is favored although reverse shock cannot be ruled out. We show that power-law outflow with Theta_obs/Theta_c > 2.5 is the best case for OA of GRB 090726. The initial Lorentz factor is Gamma_0 ~ 230-530 in case of propagation of the blast wave in a homogeneous medium, while propagation of this wave in a wind environment gives Gamma_0 ~ 80-300. The value of Gamma_0 in GRB 090726 thus falls into the lower half of the range observed in GRBs and it may even lie on the lower end. We also show that both the optical and X-ray emission decayed simultaneously and that the spectral profile from X-ray to the optical band did not vary. This OA belongs to the least luminous ones in the phase of its power-law decay corresponding to that observed for the ensemble of OAs of long GRBs.Comment: 5 pages, 5 figures, accepted to A&