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61.
Observation of the energy-level structure of the low-light adapted B800 LH4 complex by single-molecule spectroscopy 下载免费PDF全文
de Ruijter WP Oellerich S Segura JM Lawless AM Papiz M Aartsma TJ 《Biophysical journal》2004,87(5):3413-3420
Low-light adapted B800 light-harvesting complex 4 (LH4) from Rhodopseudomonas palustris is a complex in which the arrangement of the bacteriochloropyll a pigments is very different from the well-known B800-850 LH2 complex. For bulk samples, the main spectroscopic feature in the near-infrared is the occurrence of a single absorption band at 802 nm. Single-molecule spectroscopy can resolve the narrow bands that are associated with the exciton states of the individual complexes. The low temperature (1.2 K) fluorescence excitation spectra of individual LH4 complexes are very heterogeneous and display unique features. It is shown that an exciton model can adequately reproduce the polarization behavior of the complex, the experimental distributions of the number of observed peaks per complex, and the widths of the absorption bands. The results indicate that the excited states are mainly localized on one or a few subunits of the complex and provide further evidence supporting the recently proposed structure model. 相似文献
62.
Kumar MB Potter DW Hormann RE Edwards A Tice CM Smith HC Dipietro MA Polley M Lawless M Wolohan PR Kethidi DR Palli SR 《The Journal of biological chemistry》2004,279(26):27211-27218
The insect steroid hormone 20-hydroxyecdysone works through a ligand-activated nuclear receptor, the ecdysone receptor (EcR), which plays critical roles in insect development and reproduction. The EcR has been exploited to develop insecticides to control pests and gene switches for gene regulation. Recently reported crystal structures of the EcR protein show different but partially overlapping binding cavities for ecdysteroid (ECD) and diacylhydrazine (DAH) ligands, providing an explanation for the differential activity of DAH ligands in insects. 1-Aroyl-4-(arylamino)-1,2,3,4-tetrahydroquinoline (THQ) ligands were recently discovered as ecdysone agonists. Mutagenesis of the EcR (from Choristoneura fumiferana, CfEcR) ligand binding domain followed by screening in a reporter assay led to the identification of CfEcR mutants, which responded well to THQ ligands but poorly to both ECD and DAH ligands. These mutants were further improved by introducing a second mutation, A110P, which was previously reported to cause ECD insensitivity. Testing of these V128F/A110P and V128Y/A110P mutants in a C57BL/6 mouse model coactivator interaction assay and in insect cells showed that this mutant EcR is activated by THQ ligands but not by ECD or DAH ligands. The CfEcR and its V128F/A110P mutant were used to demonstrate simultaneous regulation of two reporter genes using THQ and DAH ligands. 相似文献
63.
Theoretical note: tests of synergy in sweetener mixtures 总被引:3,自引:3,他引:0
Some methods for examining the additivity of sweeteners, and their synergy
in mixtures depend upon setting component concentrations on the basis of
sweetness equivalence, usually to a sucrose reference. These methods may
under- or over-predict the sweetness of a mixture, leading to spurious
claims of synergy or mixture suppression. This paper points out one problem
with one such popular method, in that the method can lead to a conclusion
that a substance would synergize with itself. To the extent that
self-synergy is an illogical conclusion for a mixture comparison, such a
method should be avoided in tests of synergy. The sweetness equivalence
approach is contrasted with a simpler approach based on concentrations that
does not lead to conclusions of self- synergy.
相似文献
64.
The genes encoding three invariant components of the human T-cell antigen receptor, the CD3 , , and chains, are located on human chromosome 11 at band q23. We isolated cosmid clones containing the human CD3 and chain genes in vectors designed for rapid and efficient chromosome walking. The human CD3 gene was located in the region immediately downstream of the CD3 and genes using synthetic oligonucleotide probes and the localization of this gene confirmed by DNA sequencing. Detailed restriction mapping of the CD3 locus demonstrated that all three CD3 subunits are encoded within 60 kb of DNA with the CD3 gene located 26 kb downstream of the CD3 and genes. Analysis of genomic DNA on pulsed field gels using probes isolated from these cosmid clones defined a physical map of 750 kb spanning the CD3 locus on human chromosome 11g23. The CD3 genes thus comprise a multigene family encoding cell surface components important for transmembrane signaling on T lymphocytes. The arrangement of these genes suggest that they may share common regulatory elements for the control of gene expression during T-cell ontogeny. 相似文献
65.
Goldstein DB; Zhivotovsky LA; Nayar K; Linares AR; Cavalli-Sforza LL; Feldman MW 《Molecular biology and evolution》1996,13(9):1213-1218
It has recently been suggested that observed levels of variation at
microsatellite loci can be used to infer patterns of selection in genomes
and to assess demographic history. In order to evaluate the feasibility of
these suggestions it is necessary to know something about how levels of
variation at microsatellite loci are expected to fluctuate due simply to
stochasticity in the processes of mutation and inheritance (genetic
sampling). Here we use recently derived properties of the stepwise mutation
model to place confidence intervals around the variance in repeat score
that is expected at mutation-drift equilibrium and outline a statistical
test for whether an observed value differs significantly from expectation.
We also develop confidence intervals for the time course of the buildup of
variation following a complete elimination of variation, such as might be
caused by a selective sweep or an extreme population bottleneck. We apply
these methods to the variation observed at human Y-specific
microsatellites. Although a number of authors have suggested the
possibility of a very recent sweep, our analyses suggest that a sweep or
extreme bottleneck is unlikely to have occurred anytime during the last
approximately 74,000 years. To generate this result we use a recently
estimated mutation rate for microsatellite loci of 5.6 x 10(-4) along with
the variation observed at autosomal microsatellite loci to estimate the
human effective population size. This estimate is 18,000, implying an
effective number of 4,500 Y chromosomes. One important general conclusion
to emerge from this study is that in order to reject mutation-drift
equilibrium at a set of linked microsatellite loci it is necessary to have
an unreasonably large number of loci unless the observed variance is far
below that expected at mutation-drift equilibrium.
相似文献
66.
67.
Colonyzer: automated quantification of micro-organism growth characteristics on solid agar 总被引:1,自引:0,他引:1
Conor Lawless Darren J Wilkinson Alexander Young Stephen G Addinall David A Lydall 《BMC bioinformatics》2010,11(1):287
Background
High-throughput screens comparing growth rates of arrays of distinct micro-organism cultures on solid agar are useful, rapid methods of quantifying genetic interactions. Growth rate is an informative phenotype which can be estimated by measuring cell densities at one or more times after inoculation. Precise estimates can be made by inoculating cultures onto agar and capturing cell density frequently by plate-scanning or photography, especially throughout the exponential growth phase, and summarising growth with a simple dynamic model (e.g. the logistic growth model). In order to parametrize such a model, a robust image analysis tool capable of capturing a wide range of cell densities from plate photographs is required. 相似文献68.
Winnie CW Chu Wynnie MW Lam Bobby KW Ng Lam Tze-ping Kwong-man Lee Xia Guo Jack CY Cheng R Geoffrey Burwell Peter H Dangerfield Tim Jaspan 《Scoliosis》2008,3(1):1-24
There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an on-line Delphi discussion. The Statement for this debate was written by Dr WCW Chu and colleagues who examine the spinal cord to vertebral growth interaction during adolescence in scoliosis. Using the multi-planar reconstruction technique of magnetic resonance imaging they investigated the relative length of spinal cord to vertebral column including ratios in 28 girls with AIS (mainly thoracic or double major curves) and 14 age-matched normal girls. Also evaluated were cerebellar tonsillar position, somatosensory evoked potentials (SSEPs), and clinical neurological examination. In severe AIS compared with normal controls, the vertebral column is significantly longer without detectable spinal cord lengthening. They speculate that anterior spinal column overgrowth relative to a normal length spinal cord exerts a stretching tethering force between the two ends, cranially and caudally leading to the initiation and progression of thoracic AIS. They support and develop the Roth-Porter concept of uncoupled neuro-osseous growth in the pathogenesis of AIS which now they prefer to term ' asynchronous neuro-osseous growth'. Morphological evidence about the curve apex suggests that the spinal cord is also affected, and a 'double pathology' is suggested. AIS is viewed as a disorder with a wide spectrum and a common neuroanatomical abnormality namely, a spinal cord of normal length but short relative to an abnormally lengthened anterior vertebral column. Neuroanatomical changes and/or abnormal neural function may be expressed only in severe cases. This asynchronous neuro-osseous growth concept is regarded as one component of a larger concept. The other component relates to the brain and cranium of AIS subjects because abnormalities have been found in brain (infratentorial and supratentorial) and skull (vault and base). The possible relevance of systemic melatonin-signaling pathway dysfunction, platelet calmodulin levels and putative vertebral vascular biology to the asynchronous neuro-osseous growth concept is discussed. A biomechanical model to test the spinal component of the concept is in hand. There is no published research on the biomechanical properties of the spinal cord for scoliosis specimens. Such research on normal spinal cords includes movements (kinematics), stress-strain responses to uniaxial loading, and anterior forces created by the stretched cord in forward flexion that may alter sagittal spinal shape during adolescent growth. The asynchronous neuro-osseous growth concept for the spine evokes controversy. Dr Chu and colleagues respond to five other concepts of pathogenesis for AIS and suggest that relative anterior spinal overgrowth and biomechanical growth modulation may also contribute to AIS pathogenesis. 相似文献
69.
Hazel A. Tharia Thomas D. Nightingale Miroslav Z. Papiz Anna M. Lawless 《Photosynthesis research》1999,61(2):157-167
The separation of light-harvesting peptides by RP-HPLC is notoriously difficult due to the typically strong interaction of peptides with the column matrix, their relatively low solubility in the mobile phase and the tendency for non-specific aggregation during sample preparation. This paper illustrates a reproducible method for investigating the composition of four spectrally different forms of LH2 isolated from Rps. palustris. The method contrasts with previous attempts to isolate peptides from these multi-LH2 complexes and uses the well characterised B800–850 complex from Rps. acidophila as a test of reliability. Three pairs of LH2 peptides, a, b and d, were identified from Rps. palustris grown under high- (7000 lux) or intermediate- (1000 lux) light conditions. At lower light (300 and 90 lux), b was absent, and the level of a was significantly reduced. Results show that a and b peptides form the high light B800-850 complex, whereas the low light LH2 complex is only composed of d peptides and resembles the B800–820 complex from Rps. acidophila by sequence homology. The absorption spectrum of this complex has a single peak centred on 800 nm and appears to be a novel LH2 complex. At low light growth conditions, this B800 species is the predominant LH2 complex in Rps. palustris and indicates that peptide expression is a crucial factor in adapting to different light intensities. 相似文献
70.
DESCRIPTIVE ANALYSIS OF DIVALENT SALTS 总被引:2,自引:0,他引:2