Two closely related RecQ-helicases have antagonistic roles in homologous recombination and DNA repair in Arabidopsis thaliana

RecQ helicases are involved in the processing of DNA structures arising during replication, recombination, and repair throughout all kingdoms of life. Mutations of different RecQ homologues are responsible for severe human diseases, such as Blooms (BLM) or Werner (WRN) syndrome. The loss of RecQ function is often accompanied by hyperrecombination caused by a lack of crossover suppression. In the Arabidopsis genome seven different RecQ genes are present. Two of them (AtRECQ4A and 4B) arose because of a recent duplication and are still nearly 70% identical on a protein level. Knockout of these genes leads to antagonistic phenotypes: the RECQ4A mutant shows sensitivity to DNA-damaging agents, enhanced homologous recombination (HR) and lethality in a mus81 background. Moreover, mutation of RECQ4A partially suppresses the lethal phenotype of an AtTOP3alpha mutant, a phenomenon that had previously been demonstrated for RecQ homologues of unicellular eukaryotes only. Together, these facts strongly suggest that in plants RECQ4A is functionally equivalent to SGS1 of Saccharomyces cerevisiae and the mammalian BLM protein. In stark contrast, mutants of the closely related RECQ4B are not mutagen-sensitive, not viable in a mus81 background, and unable to suppress the induced lethality caused by loss of TOP3. Moreover, they are strongly impaired in HR. Thus, AtRECQ4B is specifically required to promote but not to suppress crossovers, a role in which it differs from all eukaryotic RecQ homologues known

The distribution of volatile elements during rocky planet formation

Core segregation and atmosphere formation are two of the major processes that redistribute the volatile elements—hydrogen (H), carbon (C), nitrogen (N), and sulfur (S)—in and around rocky planets during their formation. The volatile elements by definition accumulate in gaseous reservoirs and form atmospheres. However, under conditions of early planet formation, these elements can also behave as siderophiles (i.e., iron-loving) and become concentrated in core-forming metals. Current models of core formation suggest that metal-silicate reactions occurred over a wide pressure, temperature, and compositional space to ultimately impose the chemistries of the cores and silicate portions of rocky planets. Additionally, the solubilities of volatile elements in magmas determine their transfer between the planetary interiors and atmospheres, which has recently come into sharper focus in the context of highly irradiated, potentially molten exoplanets. Recently, there has been a significant push to experimentally investigate the metal-silicate and magma-gas exchange coefficients for volatile elements over a wide range of conditions relevant to rocky planet formation. Qualitatively, results from the metal-silicate partitioning studies suggest that cores of rocky planets could be major reservoirs of the volatile elements though significant amounts will remain in mantles. Results from solubility studies imply that under oxidizing conditions, most H and S are sequestered in the magma ocean, while most N is outgassed to the atmosphere, and C is nearly equally distributed between the atmosphere and the interior. Under reducing conditions, nearly all N dissolves in the magma ocean, the atmosphere becomes the dominant C reservoir, while H becomes more equally distributed between the interior and the atmosphere, and S remains dominantly in the interior. These chemical trends bear numerous implications for the chemical differentiation of rocky planets and the formation and longevity of secondary atmospheres in the early Solar System and exoplanetary systems. Further experimental and modeling efforts are required to understand the potential of chemical and physical disequilibria during core formation and magma ocean crystallization and to constrain the distributions of volatile elements in the interiors and atmospheres of rocky planets through their formation and long-term geologic evolution.</p

Variation in the attachment of Streptococcus pneumoniae to human pharyngeal epithelial cells after treatment with S-carboxymethylcysteine

S-carboxymethylcysteine (S-CMC) is a mucolytic agent that can prevent respiratory infection by decreasing the attachment of respiratory pathogens to human pharyngeal epithelial cells (HPECs). Streptococcus pneumoniae is a major cause of respiratory infections. A previous study revealed that treatment of S. pneumoniae with S-CMC caused a decrease in the attachment of this bacterium to HPECs. In the present study we found that the effect of S-CMC varied according to hosts and strains. S-CMC treatment altered the surface structure of S. pneumoniae, resulting in a decrease of attachment, without affecting the virulence of the bacteria. © 2008 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases

MC4R Variant Is Associated With BMI but Not Response to Resistance Training in Young Females

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93697/1/oby_2147_sm_1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/93697/2/oby.2010.180.pd

Off-nuclear star formation and obscured activity in the luminous infrared galaxy NGC 2623

New optical Hubble Space Telescope (HST), Spitzer Space Telescope, and XMM observations of the luminous infrared galaxy (LIRG) NGC 2623 are presented. This galaxy was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The prominent 3.2 kpc southern extension to the nucleus has been resolved by HST observations into ~100 star clusters, making it one of the richest off-nuclear concentrations of bright clusters observed in GOALS. The clusters have M_(F555W) ~-6.6 to -12.6 mag, which is within the magnitude range of Antennae galaxy clusters and in excess of 30 Doradus clusters at the high end. Their optical colors are primarily consistent with ages of ~1–100 Myr. Archival GALEX data show the off-nuclear region to be extremely bright in the far-ultraviolet, being equivalent in luminosity to the resolved nuclear region at 0.15 µm, but becoming less energetically significant at increasing wavelengths. In addition, [Ne v] 14.3 µm emission is detected with Spitzer IRS, confirming the inference from the X-ray and radio data that an active galactic nucleus (AGN) is present. Thus, the off-nuclear optical clusters are associated with a secondary burst of activity corresponding to a star formation rate ~0.1–0.2 M⊙ yr^(-1); the bulk of infrared (and thus bolometric) luminosity is generated via star formation and an AGN embedded behind dust within the inner kiloparsec of the system. If the infrared luminosity is primarily reprocessed starlight, the off-nuclear starburst accounts for <1% of the present star formation in NGC 2623

Ethylenediamine Addition Improves Performance and Suppresses Phase Instabilities in Mixed-Halide Perovskites

We show that adding ethylenediamine (EDA) to perovskite precursor solution improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA1-xCsxPb(I1-yBry)3 which are currently of interest for perovskite-on-Si tandem solar cells. Using spectroscopy and hyperspectral microscopy, we show that the additive improves film homogeneity and suppresses the phase instability that is ubiquitous in high-Br perovskite formulations, producing films that remain stable for over 100 days in ambient conditions. With the addition of 1 mol% EDA we demonstrate 1.69 eV-gap perovskite single-junction p-i-n devices with a VOC of 1.22 V, and a champion maximum power point tracked power conversion efficiency of 18.8%, comparable to the best reported methylammonium-free perovskites. Using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction techniques, we show that EDA reacts with FA+ in solution, rapidly and quantitatively forming imidazolinium cations. It is the presence of imidazolinium during crystallization which drives the improved perovskite thin-film properties