The Management of Risk - Land, Sea, Air and Space

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Modification of photosystem II activity by protein phosphorylation

AbstractPhosphorylation of proteins within pea thylakoid membranes decreases photosystem II (PSII) mediated electron transfer at saturating light intensities which, according to changes in room temperature chlorophyll fluorescence transients, is due to a modification in the electron transfer from QA to QB. However, a previously reported increase in the ability of DCMU to inhibit PS2 electron flow to DCPIP, as a consequence of protein phosphorylation, was not observed, although changes in DCMU efficacy were found to depend upon the redox state of the plastoquinone (PQ) pool

Edgar Allan Poe’s Chaotic Drive to Unity

In his philosophical prose-poem Eureka, Edgar Allan Poe argues that true unity negates physical matter. By extension, disunity is a necessary part of existence. Additionally, Poe’s theoretical essays stress the importance of the ‘unity of impression’ in writing, by which means a single effect is elaborated and sustained throughout a poem, and to which all aspects of that piece of writing contribute. With these theories in mind, this paper explores the drive towards unity in Poe’s polar fiction, the unified space as a place of revelation, and its effect on the act of writing. These stories demonstrate a complex relationship between the antithetical states of unity and disunity; whirlpools in particular become a symbol for this space where unity and disunity coexist. Poe’s voyagers are forced to make a choice between achieving unity, and with it ultimate knowledge, at the expense of communicating their discovery, and abandoning their quest and returning with nothing to communicate

Repression of CIITA by the Epstein-Barr virus transcription factor Zta is independent of its dimerization and DNA binding

Repression of the cellular CIITA gene is part of the immune evasion strategy of the γherpes virus Epstein-Barr virus (EBV) during its lytic replication cycle in B-cells. In part this is mediated through down regulation of MHC class II gene expression via the targeted repression of CIITA, the cellular master regulator of MHC class II gene expression. The repression is achieved through a reduction in CIITA promoter activity initiated by the EBV transcription and replication factor Zta (BZLF1, EB1, ZEBRA). Zta is the earliest gene expressed during the lytic replication cycle. Zta interacts with sequence specific elements in promoters, enhancers and the replication origin (ZREs) and also modulates gene expression through interaction with cellular transcription factors and co-activators. Here we explore the requirements for Zta-mediated repression of the CIITA promoter. We find that repression by Zta is specific for the CIITA promoter and can be achieved in the absence of other EBV genes. Surprisingly, we find that the dimerization region of Zta is not required to mediate repression. This contrasts with an obligate requirement of this region to correctly orientate the DNA contact regions of Zta to mediate activation of gene expression through ZREs. Additional support for the model that Zta represses the CIITA promoter without direct DNA binding comes from promoter mapping that shows that repression does not require the presence of a ZRE in the CIITA promoter

Isotropic Mid-Infrared Emission from the Central 100 pc of Active Galaxies

Dust reprocesses the intrinsic radiation of active galactic nuclei (AGNs) to emerge at longer wavelengths. The observed mid-infrared (MIR) luminosity depends fundamentally on the luminosity of the central engine, but in detail it also depends on the geometric distribution of the surrounding dust. To quantify this relationship, we observe nearby normal AGNs in the MIR to achieve spatial resolution better than 100 pc, and we use absorption-corrected X-ray luminosity as a proxy for the intrinsic AGN emission. We find no significant difference between optically classified Seyfert 1 and 2 galaxies. Spectroscopic differences, both at optical and IR wavelengths, indicate that the immediate surroundings of AGNs is not spherically symmetric, as in standard unified AGN models. A quantitative analysis of clumpy torus radiative transfer models shows that a clumpy local environment can account for this dependence on viewing geometry while producing MIR continuum emission that remains nearly isotropic, as we observe, although the material is not optically thin at these wavelengths. We find some luminosity dependence on the X-ray/MIR correlation in the smallest scale measurements, which may indicate enhanced dust emission associated with star formation, even on these sub-100 pc scales.Comment: 10 pages, 5 figures; accepted for publication in Ap