Water vapour in the atmosphere of a transiting extrasolar planet

Water is predicted to be among, if not the most abundant molecular species after hydrogen in the atmospheres of close-in extrasolar giant planets (hot-Jupiters) Several attempts have been made to detect water on an exoplanet, but have failed to find compelling evidence for it or led to claims that should be taken with caution. Here we report an analysis of recent observations of the hot-Jupiter HD189733b taken during the transit, where the planet passed in front of its parent star. We find that absorption by water vapour is the most likely cause of the wavelength-dependent variations in the effective radius of the planet at the infrared wavelengths 3.6, 5.8 and 8 microns. The larger effective radius observed at visible wavelengths may be due to either star variability or the presence of clouds/hazes. We explain the most recent thermal infrared observations of the planet during secondary transit behind the star, reporting a non-detection of water on HD189733b, as being a consequence of the nearly isothermal vertical profile of the planet.s atmosphere. Our results show that water is detectable on extrasolar planets using the primary transit technique and that the infrared should be a better wavelength region than the visible, for such searches

Recombination Phenotypes of Escherichia coli greA Mutants

<p>Abstract</p> <p>Background</p> <p>The elongation factor GreA binds to RNA polymerase and modulates transcriptional pausing. Some recent research suggests that the primary role of GreA may not be to regulate gene expression, but rather, to promote the progression of replication forks which collide with RNA polymerase, and which might otherwise collapse. Replication fork collapse is known to generate dsDNA breaks, which can be recombinogenic. It follows that GreA malfunction could have consequences affecting homologous recombination.</p> <p>Results</p> <p><it>Escherichia coli </it>mutants bearing substitutions of the active site acidic residues of the transcription elongation factor GreA, D41N and E44K, were isolated as suppressors of growth inhibition by a toxic variant of the bacteriophage lambda Red-beta recombination protein. These mutants, as well as a D41A <it>greA </it>mutant and a <it>greA </it>deletion, were tested for proficiency in recombination events. The mutations were found to increase the efficiency of RecA-RecBCD-mediated and RecA-Red-mediated recombination, which are replication-independent, and to decrease the efficiency of replication-dependent Red-mediated recombination.</p> <p>Conclusion</p> <p>These observations provide new evidence for a role of GreA in resolving conflicts between replication and transcription.</p

Structural basis for the bacterial transcription-repair coupling factor/RNA polymerase interaction

The transcription-repair coupling factor (TRCF, the product of the mfd gene) is a widely conserved bacterial protein that mediates transcription-coupled DNA repair. TRCF uses its ATP-dependent DNA translocase activity to remove transcription complexes stalled at sites of DNA damage, and stimulates repair by recruiting components of the nucleotide excision repair pathway to the site. A protein/protein interaction between TRCF and the β-subunit of RNA polymerase (RNAP) is essential for TRCF function. CarD (also called CdnL), an essential regulator of rRNA transcription in Mycobacterium tuberculosis, shares a homologous RNAP interacting domain with TRCF and also interacts with the RNAP β-subunit. We determined the 2.9-Å resolution X-ray crystal structure of the RNAP interacting domain of TRCF complexed with the RNAP-β1 domain, which harbors the TRCF interaction determinants. The structure reveals details of the TRCF/RNAP protein/protein interface, providing a basis for the design and interpretation of experiments probing TRCF, and by homology CarD, function and interactions with the RNAP

Paclitaxel-induced peripheral neuropathy is caused by epidermal ROS and mitochondrial damage through conserved MMP-13 activation

Paclitaxel induces peripheral neuropathy as a side effect of cancer treatment. The underlying causes are unclear, but epidermal, unmyelinated axons have been shown to be the first to degenerate. We previously utilized an in vivo zebrafish model to show that the epidermal matrix-metalloproteinase 13 (MMP-13) induces degeneration of unmyelinated axons, whereas pharmacological inhibition of MMP-13 prevented axon degeneration. However, the precise functions by which MMP-13 is regulated and affects axons remained elusive. In this study, we assessed mitochondrial damage and reactive oxygen species (ROS) formation as possible inducers of MMP-13, and we analyzed MMP-13-dependent damage. We show that the small ROS, HO, is increased in basal keratinocytes following treatment with paclitaxel. Cytoplasmic HOappears to derive, at least in part, from mitochondrial damage, leading to upregulation of MMP-13, which in turn underlies increased epidermal extracellular matrix degradation. Intriguingly, also axonal mitochondria show signs of damage, such as fusion/fission defects and vacuolation, but axons do not show increased levels of HO. Since MMP-13 inhibition prevents axon degeneration but does not prevent mitochondrial vacuolation, we suggest that vacuolization occurs independently of axonal damage. Finally, we show that MMP-13 dysregulation also underlies paclitaxel-induced peripheral neuropathy in mammals, indicating that epidermal mitochondrial HOand its effectors could be targeted for therapeutic interventions

Paclitaxel-induced peripheral neuropathy is caused by epidermal ROS and mitochondrial damage through conserved MMP-13 activation

Abstract Paclitaxel is a chemotherapeutic agent that causes peripheral neuropathy (PIPN) as a side effect of cancer treatment. Severely affected patients need to terminate chemotherapy, diminishing their chance of survival. The underlying causes of PIPN are unclear, but epidermal, unmyelinated axons have been shown to be the first to degenerate. We previously utilized a zebrafish in vivo model to show that the epidermal matrix-metalloproteinase 13 (MMP-13) induces degeneration of unmyelinated axons, whereas pharmacological inhibition of MMP-13 prevented axon degeneration. The precise functions by which MMP-13 is regulated and affects axons, however, remained elusive. In this study, we assessed mitochondrial damage and reactive oxygen species (ROS) formation as possible inducers of MMP-13, and we analyzed MMP-13-dependent damage. We show that the small ROS, H 2 O 2 , is increased in keratinocytes following treatment with paclitaxel. Epidermal mitochondrial damage appears to be a source of ROS leading to cytoplasmic H 2 O 2 elevation, upregulation of MMP-13, and increased matrix degradation. Intriguingly, although axonal mitochondria also show aberrant morphologies and are vacuolized, as shown in other neuropathies, these axonal mitochondria do not produce increased H 2 O 2 levels. We suggest that mitochondrial vacuolization occurs independently of axonal damage given that MMP-13 inhibition prevents axon degeneration, though vacuoles persist. We further show that MMP-13 dysregulation also underlies PIPN in rodent paclitaxel models, and that this function appears to be DRG neuron-extrinsic. These findings suggest that vacuolization is not a cause of paclitaxel-induced neuropathy, and that epidermal MMP-13 is a strong candidate for therapeutic interventions in cancer patients with neuropathy