排序方式: 共有34条查询结果,搜索用时 15 毫秒
1.
JACQUES Destombes ET JEAN-LOUIS Henry 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1987,20(2):129-139
A re-examination of the trilobite Baniaspis globosa Destombes (Phacopina) from the Ashgill of the Anti-Atlas (Morocco) shows that it has several derived characters which allow us to classify it in the family Calmoniidae. Calmoniids were characteristic members of the Malvino-Kaffric province during the Lower Devonian. Hence we regard the origins of this palaeogeographic province as located on the northern Gondwanan margin as early as Ashgill, or even Caradoc, times. We agree with those authors who have suggested that the trilobite associations present in the Anti-Atlas, the Montagne Noire (France) and Bohemia during the earlier Ordovician argue against the existence of a 'proto-Tethys' ocean. 相似文献
2.
JEAN-LOUIS HENRY ET JACQUES DESTOMBES 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1991,24(3):249-253.
During the Llandeilo, the sandy lithological units which develop locally in the Armorican Massif, Spain and Morocco, are all characterized by similar trilobite associations in which endobenthic homalonotids. well adapted to shallow water and sandy substrate, are predominant. During the Llandeilo, on the northern Gondwanan margin, the wide geographical distribution of most of the trilobites, controlled by environmental factors, shows that the existence of a 'Proto-Tethys' ocean is unlikely. □ North Gondwana, Trilobita, Homalonotidae, Ordovician, Llandeilo. palaeoenvironment. 相似文献
3.
Out of Africa and back again: nested cladistic analysis of human Y chromosome variation 总被引:18,自引:3,他引:15
Hammer MF; Karafet T; Rasanayagam A; Wood ET; Altheide TK; Jenkins T; Griffiths RC; Templeton AR; Zegura SL 《Molecular biology and evolution》1998,15(4):427-441
We surveyed nine diallelic polymorphic sites on the Y chromosomes of 1,544
individuals from Africa, Asia, Europe, Oceania, and the New World.
Phylogenetic analyses of these nine sites resulted in a tree for 10
distinct Y haplotypes with a coalescence time of approximately 150,000
years. The 10 haplotypes were unevenly distributed among human populations:
5 were restricted to a particular continent, 2 were shared between Africa
and Europe, 1 was present only in the Old World, and 2 were found in all
geographic regions surveyed. The ancestral haplotype was limited to African
populations. Random permutation procedures revealed statistically
significant patterns of geographical structuring of this paternal genetic
variation. The results of a nested cladistic analysis indicated that these
geographical associations arose through a combination of processes,
including restricted, recurrent gene flow (isolation by distance) and range
expansions. We inferred that one of the oldest events in the nested
cladistic analysis was a range expansion out of Africa which resulted in
the complete replacement of Y chromosomes throughout the Old World, a
finding consistent with many versions of the Out of Africa Replacement
Model. A second and more recent range expansion brought Asian Y chromosomes
back to Africa without replacing the indigenous African male gene pool.
Thus, the previously observed high levels of Y chromosomal genetic
diversity in Africa may be due in part to bidirectional population
movements. Finally, a comparison of our results with those from nested
cladistic analyses of human mtDNA and beta-globin data revealed different
patterns of inferences for males and females concerning the relative roles
of population history (range expansions) and population structure
(recurrent gene flow), thereby adding a new sex-specific component to
models of human evolution.
相似文献
4.
Discovery and structural characterization of an allosteric inhibitor of bacterial cis‐prenyltransferase
下载免费PDF全文
![点击此处可从《Protein science : a publication of the Protein Society》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dennis E. Danley Eric T. Baima Mahmoud Mansour Kimberly F. Fennell Boris A. Chrunyk John P. Mueller Shenping Liu Xiayang Qiu 《Protein science : a publication of the Protein Society》2015,24(1):20-26
Undecaprenyl pyrophosphate synthase (UPPs) is an essential enzyme in a key bacterial cell wall synthesis pathway. It catalyzes the consecutive condensations of isopentenyl pyrophosphate (IPP) groups on to a trans-farnesyl pyrophosphate (FPP) to produce a C55 isoprenoid, undecaprenyl pyrophosphate (UPP). Here we report the discovery and co-crystal structures of a drug-like UPPs inhibitor in complex with Streptococcus pneumoniae UPPs, with and without substrate FPP, at resolutions of 2.2 and 2.1 Å, respectively. The UPPs inhibitor has a low molecular weight (355 Da), but displays potent inhibition of UPP synthesis in vitro (IC50 50 nM) that translates into excellent whole cell antimicrobial activity against pathogenic strains of Streptococcal species (MIC90 0.4 µg mL−1). Interestingly, the inhibitor does not compete with the substrates but rather binds at a site adjacent to the FPP binding site and interacts with the tail of the substrate. Based on the structures, an allosteric inhibition mechanism of UPPs is proposed for this inhibitor. This inhibition mechanism is supported by biochemical and biophysical experiments, and provides a basis for the development of novel antibiotics targeting Streptococcus pneumoniae. 相似文献
5.
Herwig Bachmann Douwe Molenaar Michiel Kleerebezem Johan ET van Hylckama Vlieg 《The ISME journal》2011,5(5):929-932
Cooperative behavior is widely spread in microbial populations. An example is the expression of an extracellular protease by the lactic acid bacterium Lactococcus lactis, which degrades milk proteins into free utilizable peptides that are essential to allow growth to high cell densities in milk. Cheating, protease-negative strains can invade the population and drive the protease-positive strain to extinction. By using multiple experimental approaches, as well as modeling population dynamics, we demonstrate that the persistence of the proteolytic trait is determined by the fraction of the generated peptides that can be captured by the cell before diffusing away from it. The mechanism described is likely to be relevant for the evolutionary stability of many extracellular substrate-degrading enzymes. 相似文献
6.
As a first step towards understanding the process of blue light perception, and the signal transduction mechanisms involved, in Neurospora crassa we have used a pharmacological approach to screen a wide range of second messengers and chemical compounds known to interfere with the activity of well-known signal transducing molecules in vivo. We tested the influence of these compounds on the induction of the al-3 gene, a key step in light-induced carotenoid biosynthesis. This approach has implicated protein kinase C (PKC) as a component of the light transduction machinery. The conclusion is based on the effects of specific inhibitors (calphostin C and chelerythrine chloride) and activators of PKC (1,2-dihexanoyl-sn-glycerol). During vegetative growth PKC may be responsible for desensitization to light because inhibitors of the enzyme cause an increase in the total amount of mRNA transcribed after illumination. PKC is therefore proposed here to be an important regulator of transduction of the blue light signal, and may act through modification of the protein White Collar-1, which we show to be a substrate for PKC in N. crassa. 相似文献
7.
8.
Waka Yokoyama Hitoshi Kohsaka Kayoko Kaneko Matthew Walters Aiko Takayasu Shin Fukuda Chie Miyabe Yoshishige Miyabe Paul E Love Nobuhiro Nakamoto Takanori Kanai Kaori Watanabe-Imai Trevor T Charvat Mark ET Penfold Juan Jaen Thomas J Schall Masayoshi Harigai Nobuyuki Miyasaka Toshihiro Nanki 《Arthritis research & therapy》2014,16(5)
Introduction
Biological drugs are effective in patients with rheumatoid arthritis (RA), but increase severe infections. The CC chemokine receptor (CCR) 9 antagonist was effective for Crohn’s disease without critical adverse effects including infections in clinical trials. The present study was carried out to explore the pathogenic roles of chemokine (C-C motif) ligand (CCL) 25 and its receptor, CCR9, in autoimmune arthritis and to study if the CCR9 antagonist could be a new treatment for RA.Methods
CCL25 and CCR9 expression was examined with immunohistochemistry and Western blotting. Concentration of interleukin (IL)-6, matrix metalloproteinase (MMP)-3 and tumor necrosis factor (TNF)-α was measured with enzyme-linked immunosorbent assays. Effects of abrogating CCR9 on collagen-induced arthritis (CIA) was evaluated using CCR9-deficient mice or the CCR9 antagonist, CCX8037. Fluorescence labeled-CD11b+ splenocytes from CIA mice were transferred to recipient CIA mice and those infiltrating into the synovial tissues of the recipient mice were counted.Results
CCL25 and CCR9 proteins were found in the RA synovial tissues. CCR9 was expressed on macrophages, fibroblast-like synoviocytes (FLS) and dendritic cells in the synovial tissues. Stimulation with CCL25 increased IL-6 and MMP-3 production from RA FLS, and IL-6 and TNF-α production from peripheral blood monocytes. CIA was suppressed in CCR9-deficient mice. CCX8037 also inhibited CIA and the migration of transferred CD11b+ splenocytes into the synovial tissues.Conclusions
The interaction between CCL25 and CCR9 may play important roles in cell infiltration into the RA synovial tissues and inflammatory mediator production. Blocking CCL25 or CCR9 may represent a novel safe therapy for RA. 相似文献9.
PIERRE MOISSETTE ET JEAN-PAUL SAINT MARTIN 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1995,28(3):271-283
Moissette, P. & Saint Martin, J:P. 1995 11 30 Bryozoaires des milieux récifaux miocenes du sillon sud-rifain au Maroc. [Bryozoans from Miocene reef environments in the South-Rifian corridor of Morocco. In late Miocene coral reefs from the Fes area (Northern Morocco), bryozoans are the best-represented group. An inventory of the bryozoan fauna (59 species) was taken on two reefs with different organization and palaeogeographical situation in a late Miocene seaway between the Atlantic and the Mediterranean. A study of the bryozoans and their zoarial forms allows an improved reconstruction of reefal environments and available habitats. Membraniporiforrn (encrusting) colonies largely predominate, whereas celleporiforms (nodular colonies) are more rare. Rigid erect (vinculariiform, adeoniform, and reteporiform) and rigid articulated zoarial types (cellariiform and catenicelliform) are fairly well represented. At depths of about 10 m and on the reef front encrusting bryozoans were well developed in cryptic habitats on living coral substrates. Erect species lived in cavities provided by the coral framework, and plants offered flexible substrates for the attachment of epiphytal forms. □Bryozoa, coral reefs, Morocco, Messininn, pulueoecology. Dans les récifs coralliens du Miocène supérieur de la région de Fes (Maroc septentrional), les bryozoaires constituent, parrni les organismes conservés, le groupe le mieux représenté. Un recensement de la fame de bryozoaires (59 espèces) a été effectué dans deux récifs d'organisation et de situation paléogéographique différentes, dans un secteur de communication entre Atlantique et Méditerranée au MiocéFne supérieur. L'étude des bryozoaires et de leurs formes zoariales permet de proposer une meilleure reconstitution de I'environnement récifal et des habitats disponibles. Les colonies membraniporiformes (encrobtantes) predominent largement, alors que les cellepori-formes (colonies noduleuses) sont beaucoup plus rares. Les types zoariaux érigés rigides (vincula-riiforme, adéoniforme et rétéporiforme) et érigés articulés (cellariiforme et catenicelliforme) sont assez bien représentés. A des profondeurs denviron 10 m et dans la partie antérieure des constructions récifales, les bryozoaires encroûtants étaient bien développés dans des habitats cryptiques sur substrats coralliens vivants. Des formes dressées vivaient dans les cavités ménagées par le bâti corallien et des supports végétaux permettaient également la fixation de formes épiphytes. □Bryozouires, récifs coralliens, Muroc, Messinien, puléoécologie. 相似文献
10.
Eric T. Baima Julia A. Guzova Sumathy Mathialagan Eva E. Nagiec Medora M. Hardy Lily R. Song Sheri L. Bonar Robin A. Weinberg Shaun R. Selness Scott S. Woodard Jill Chrencik William F. Hood John F. Schindler Nandini Kishore Gabriel Mbalaviele 《The Journal of biological chemistry》2010,285(18):13498-13506