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991.
A SecY Homologue Is Required for the Elaboration of the Chloroplast Thylakoid Membrane and for Normal Chloroplast Gene Expression 总被引:4,自引:0,他引:4 下载免费PDF全文
Results of in vitro and genetic studies have provided evidence for four pathways by which proteins are targeted to the chloroplast thylakoid membrane. Although these pathways are initially engaged by distinct substrates and involve some distinct components, an unresolved issue has been whether multiple pathways converge on a common translocation pore in the membrane. A homologue of eubacterial SecY called cpSecY is localized to the thylakoid membrane. Since SecY is a component of a protein-translocating pore in bacteria, cpSecY likely plays an analogous role. To explore the role of cpSecY, we obtained maize mutants with transposon insertions in the corresponding gene. Null cpSecY mutants exhibit a severe loss of thylakoid membrane, differing in this regard from mutants lacking cpSecA. Therefore, cpSecY function is not limited to a translocation step downstream of cpSecA. The phenotype of cpSecY mutants is also much more pleiotropic than that of double mutants in which both the cpSecA- and ΔpH-dependent thylakoid-targeting pathways are disrupted. Therefore, cpSecY function is likely to extend beyond any role it might play in these targeting pathways. CpSecY mutants also exhibit a defect in chloroplast translation, revealing a link between chloroplast membrane biogenesis and chloroplast gene expression. 相似文献
992.
James L. Corbin Kenneth F. Miller Narayanankutty Pariyadath Scot Wherland Alice E. Bruce Edward I. Stiefel 《Inorganica chimica acta》1984,90(1):41-51
New linear and tripodal tetradentate ligands, LH2, are reported and their syntheses are described. The new linear ligands L = HSCH2CH2SCH2CH2NRCH2CR2SH, R = H, CH3) and the new tripodal ligands N(CH2CH2SH)2CH2Z, Z = CH2NH2, CH2N(CH3)2, CH2N(C2H5)2, CH2SCH3 and CO2- were synthesized. The known linear ligands HSCH2CH2NCH3(CH2)nNCH3CH2CH2SH (n = 2, 3) and HSCR2CH2NHCH2CH2NHCH2CR2SH (R = H, CH3) were also utilized. These ligands react with MoO2(acac)2 in CH3OH to yield MoO2L complexes in high yield. Infra-red and 1H nmr spectra provide evidence to supplement X-ray crystallographic results reported elsewhere for selected numbers of the series. Octahedral structures with cis MoO22+ groupings are assigned. Solution 1H nmr studies are consistent with a trans placement of the two thiolate donors in agreement with the X-ray studies. 相似文献
993.
Stuart R Hawtin Victoria J Wesley John Simms Rosemary A Parslow Alice Miles Kim McEwan Mary Keen Mark Wheatley 《European journal of biochemistry》2003,270(23):4681-4688
Defining how the agonist-receptor interaction differs from that of the antagonist-receptor and understanding the mechanisms of receptor activation are fundamental issues in cell signalling. The V1a vasopressin receptor (V1aR) is a member of a family of related G-protein coupled receptors that are activated by neurohypophysial peptide hormones, including vasopressin (AVP). It has recently been reported that an arginyl in the distal N-terminus of the V1aR is critical for binding agonists but not antagonists. To determine specific features required at this locus to support high affinity agonist binding and second messenger generation, Arg46 was substituted by all other 19 encoded amino acids. Our data establish that there is an absolute requirement for arginyl, as none of the [R46X]V1aR mutant constructs supported high affinity agonist binding and all 19 had defective signalling. In contrast, all of the mutant receptors possessed wildtype binding for both peptide and nonpeptide antagonists. The ratio of Ki to EC50, an indicator of efficacy, was increased for all substitutions. Consequently, although [R46X]V1aR constructs have a lower affinity for agonist, once AVP has bound all 19 are more likely than the wildtype V1aR to become activated. Therefore, in the wildtype V1aR, Arg46 constrains the inactive conformation of the receptor. On binding AVP this constraint is alleviated, promoting the transition to active V1aR. Our findings explain why arginyl is conserved at this locus throughout the evolutionary lineage of the neurohypophysial peptide hormone receptor family of G-protein coupled receptors. 相似文献
994.
Todd C. LaJeunesse Georgina Lambert Robert A. Andersen Mary Alice Coffroth David W. Galbraith 《Journal of phycology》2005,41(4):880-886
Using flow cytometric analysis of fluorescence, we measured the genome sizes of 18 cultured “free‐living” species and 29 Symbiodinium spp. isolates cultured from stony corals, gorgonians, anemones, jellyfish, and giant clams. Genome size directly correlated with cell size, as documented previously for most eukaryotic cell lines. Among the smallest of dinoflagellates, Symbiodinium spp. (6–15 μm) possessed the lowest DNA content that we measured (1.5–4.8 pg·cell?1). Bloom‐forming or potentially harmful species in the genera Alexandrium, Karenia, Pfiesteria, and Prorocentrum possessed genomes approximately 2 to 50 times larger in size. A phylogenetic analysis indicated that genome/cell size has apparently increased and decreased repeatedly during the evolution of dinoflagellates. In contrast, genome sizes were relatively consistent across distantly and closely related Symbiodinium spp. This may be the product of intracellular host habitats imposing strong selective pressures that have restricted symbiont size. 相似文献
995.
Mike Cauchy Sophie D'Aoust Brian Dawson Harold Rode Mary Alice Hefford 《Biologicals》2002,30(3):175-185
To be both safe and effective, a therapeutic product must have the correct chemical structure and be free of harmful contaminants. Structure in protein therapeutic products, however, implies not only the correct sequence of amino acids (primary structure) but also the proper folding of that amino acid chain in three-dimensional space (tertiary structure). This work is part of a general strategy to develop a battery of physico-chemical methods that could give assurances of structure (and hence function) in formulated therapeutic proteins in the absence of in vivo data. It focuses on recombinant human growth hormone (rhGH), a well-characterized therapeutic protein, and examines the utility of thermodynamic parameters in assessing its tertiary structure. Resistance of solutions of formulated rhGH to thermal denaturation was followed using Fourier Transform Infrared Spectroscopy (FTIR) by observing decreases in total helicity and increases in intermolecular beta-sheet formation. Under conditions known to induce changes in the intra-molecular ionic and H-bonding patterns stabilizing the tertiary structure but not affecting the protein's secondary structure or global fold, we have observed upwards of a 12 degrees C shift in the melting temperature of the protein. Furthermore, our results indicated that the T(m) of unfolding of rhGH was sensitive to much more subtle changes in the protein structure. Thus, resistance to thermal denaturation may well be a useful means to measure structure in formulations of well-characterized therapeutic proteins. 相似文献
996.
Extending the Namibian protected area network to safeguard hotspots of endemism and diversity 总被引:1,自引:0,他引:1
Phoebe Barnard Christopher J. Brown Alice M. Jarvis Antony Robertson Leon Van Rooyen 《Biodiversity and Conservation》1998,7(4):531-547
Namibia's state protected area network (PAN) covers 13.8% of the country's land area, but is seriously inadequate as a basis for effective biodiversity conservation. The early parks system was not designed with biological diversity in mind, and reflects instead a history of ideological, economic and veterinary considerations. Currently, parks in the Namib Desert biome make up 69% of the PAN, while savanna and woodland biomes are somewhat underrepresented (7.5 and 8.4% of their respective land areas), and the Karoo biome is badly underrepresented (1.6%). Four of 14 desert vegetation types are comprehensively protected, with 67 to 94% representation in the PAN, yet six savanna types have 0 to 2% representation by area. Mountain Savanna, a vegetation type unique to Namibia, is wholly unprotected. The status of two marine reserves, which in theory protect only 0.01% of Namibia's marine environment, needs clarification and augmentation with new reserves. Nearly 85% of Namibia's land is zoned for agriculture, so effective biodiversity protection means working outside the PAN to improve the sustainability and diversity of farming practices. Wildlife conservancies on commercial and communal farmlands show excellent potential to mitigate the ecological skew in the state PAN, with the ecological management of large areas being decentralized to rural communities in habitats otherwise neglected for conservation. Two important endemism zones, the Kaoko escarpment and coastal plain and the Sperrgebiet succulent steppe, plus the species-rich Caprivi area, offer three valuable opportunities for regional consolidation of protected areas into transboundary 'peace parks' or biosphere reserves. 相似文献
997.
Abstract: Binding of 1-[1-(2-[3 H]thienyl)cyclohexyl]piperidine ([3 H]TCP) to mouse brain and spinal cord membranes was studied using compounds selective for the NMDA-coupled 1-(1-phenylcyclohexyl)piperidine (PCP) and/or σ recognition sites. In both tissues, [3 H]TCP labeled two populations of binding sites. Density of the low-affinity sites was approximately the same in both tissues, but the population of the high-affinity [3 H]TCP sites was three times bigger in the brain than in the spinal cord. Self- and cross-displacement studies showed that the high-affinity [3 H]TCP binding sites could be identical with NMDA receptor-coupled PCP sites, whereas the low-affinity [3 H]TCP sites may be associated with σ binding sites in both tissues. The NMDA-coupled PCP sites labeled in the presence of 6.25 n M [3 H]TCP constituted a much higher percentage of the total binding in the brain (75%) than in the spinal cord (44%). Consistent with this, reintroduction of glycine and glutamate significantly increased, but DA antagonists significantly inhibited [3 H]TCP binding in the brain but not in the spinal cord. Together, these data suggest that a large component of [3 H]TCP-labeled binding sites in the spinal cord may be associated with σ but not the NMDA receptor-coupled PCP sites. 相似文献
998.
999.
Alice Risely Nadine Müller-Klein Dominik W. Schmid Kerstin Wilhelm Tim H. Clutton-Brock Marta B. Manser Simone Sommer 《Global Change Biology》2023,29(20):5816-5828
Climate change and climate-driven increases in infectious disease threaten wildlife populations globally. Gut microbial responses are predicted to either buffer or exacerbate the negative impacts of these twin pressures on host populations. However, examples that document how gut microbial communities respond to long-term shifts in climate and associated disease risk, and the consequences for host survival, are rare. Over the past two decades, wild meerkats inhabiting the Kalahari have experienced rapidly rising temperatures, which is linked to the spread of tuberculosis (TB). We show that over the same period, the faecal microbiota of this population has become enriched in Bacteroidia and impoverished in lactic acid bacteria (LAB), a group of bacteria including Lactococcus and Lactobacillus that are considered gut mutualists. These shifts occurred within individuals yet were compounded over generations, and were better explained by mean maximum temperatures than mean rainfall over the previous year. Enriched Bacteroidia were additionally associated with TB exposure and disease, the dry season and poorer body condition, factors that were all directly linked to reduced future survival. Lastly, abundances of LAB taxa were independently and positively linked to future survival, while enriched taxa did not predict survival. Together, these results point towards extreme temperatures driving an expansion of a disease-associated pathobiome and loss of beneficial taxa. Our study provides the first evidence from a longitudinally sampled population that climate change is restructuring wildlife gut microbiota, and that these changes may amplify the negative impacts of climate change through the loss of gut mutualists. While the plastic response of host-associated microbiotas is key for host adaptation under normal environmental fluctuations, extreme temperature increases might lead to a breakdown of coevolved host–mutualist relationships. 相似文献
1000.
Fabienne Maihoff Nicolas Friess Bernhard Hoiss Christian Schmid-Egger Janika Kerner Johann Neumayer Sebastian Hopfenmüller Claus Bässler Jörg Müller Alice Classen 《Diversity & distributions》2023,29(2):272-288