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排序方式: 共有134条查询结果,搜索用时 15 毫秒
71.
Phan G Remaut H Wang T Allen WJ Pirker KF Lebedev A Henderson NS Geibel S Volkan E Yan J Kunze MB Pinkner JS Ford B Kay CW Li H Hultgren SJ Thanassi DG Waksman G 《Nature》2011,474(7349):49-53
Type 1 pili are the archetypal representative of a widespread class of adhesive multisubunit fibres in Gram-negative bacteria. During pilus assembly, subunits dock as chaperone-bound complexes to an usher, which catalyses their polymerization and mediates pilus translocation across the outer membrane. Here we report the crystal structure of the full-length FimD usher bound to the FimC-FimH chaperone-adhesin complex and that of the unbound form of the FimD translocation domain. The FimD-FimC-FimH structure shows FimH inserted inside the FimD 24-stranded β-barrel translocation channel. FimC-FimH is held in place through interactions with the two carboxy-terminal periplasmic domains of FimD, a binding mode confirmed in solution by electron paramagnetic resonance spectroscopy. To accommodate FimH, the usher plug domain is displaced from the barrel lumen to the periplasm, concomitant with a marked conformational change in the β-barrel. The amino-terminal domain of FimD is observed in an ideal position to catalyse incorporation of a newly recruited chaperone-subunit complex. The FimD-FimC-FimH structure provides unique insights into the pilus subunit incorporation cycle, and captures the first view of a protein transporter in the act of secreting its cognate substrate. 相似文献
72.
Qu Chen XiuMing Liu F. Heller Ann M. Hirt Bin Lü XueLian Guo XueGang Mao JiaSheng Chen GuoYong Zhao Hua Feng Hui Guo 《科学通报(英文版)》2012,57(15):1844-1855
The magnetic susceptibility of loess from the Ily Basin,northwestern China shows maximum values in S0 paleosols but minimum values in other paleosols,the mechanism of which has been well debated.In this work,systematic magnetic measurements were made on a representative section from Neleke county.The results show that the loess horizons(L1,L2 and L3) have multi-domain magnetite grains of aeolian origin,S0 is characterized by production of pedogenetic ultrafine-grained ferrimagnetic minerals,and the other paleosols(S1,S2,and S3) are characterized by the formation of nonferrimagnetic minerals associated with waterlogging.The correlation between the low concentration of ferrimagnets,high paramagnetic content,high magnetic coercivity remanence,fine ferrimagnetic grain size and intensified pedogenesis suggest two competing processes of pedogenetic enhancement and pedogenetic depletion in the lower paleosols.Pedogenetic depletion dominates and is responsible for the low susceptibility.Changes in magnetic grain size distribution occur during pedogenetic depletion.The susceptibility variations are of multiple origins in the loess of the Ily Basin.Pedogenetic enhancement,pedogenetic depletion,and allochthonous input of magnetic minerals should all be taken into account to explain the variations of magnetic parameters. 相似文献
73.
Arthropod head segments offer a paradigm for understanding the diversification of form during evolution, as a variety of morphologically diverse appendages have arisen from them. There has been long-running controversy, however, concerning which head appendages are homologous among arthropods, and from which ancestral arrangement they have been derived. This controversy has recently been rekindled by the proposition that the probable ancestral arrangement, with appendages on the first head segment, has not been lost in all extant arthropods as previously thought, but has been retained in the pycnogonids, or sea spiders. This proposal was based on the neuroanatomical analysis of larvae from the sea spider Anoplodactylus sp., and suggested that the most anterior pair of appendages, the chelifores, are innervated from the first part of the brain, the protocerebrum. Our examination of Hox gene expression in another sea spider, Endeis spinosa, refutes this hypothesis. The anterior boundaries of Hox gene expression domains place the chelifore appendages as clearly belonging to the second head segment, innervated from the second part of the brain, the deutocerebrum. The deutocerebrum must have been secondarily displaced towards the protocerebrum in pycnogonid ancestors. As anterior-most appendages are also deutocerebral in the other two arthropod groups, the Euchelicerata and the Mandibulata, we conclude that the protocerebral appendages have been lost in all extant arthropods. 相似文献
74.
Unrepaired lesions in the DNA template pose a threat to accurate replication. Several pathways exist in Escherichia coli to reactivate a blocked replication fork. The process of recombination-dependent restart of broken forks is well understood, but the consequence of replication through strand-specific lesions is less well known. Here we show that replication can be restarted and leading-strand synthesis re-initiated downstream of an unrepaired block to leading-strand progression, even when the 3'-OH of the nascent leading strand is unavailable. We demonstrate that the loading by a replication restart system of a single hexamer of the replication fork helicase, DnaB, on the lagging-strand template is sufficient to coordinate priming by the DnaG primase of both the leading and lagging strands. These observations provide a mechanism for damage bypass during fork reactivation, demonstrate how daughter-strand gaps are generated opposite leading-strand lesions during the replication of ultraviolet-light-irradiated DNA, and help to explain the remarkable speed at which even a heavily damaged DNA template is replicated. 相似文献
75.
Is guanosine diphosphate-D-glucose a precursor of cellulose? 总被引:2,自引:0,他引:2
76.
E. Fischer H. Spatz B. Heller H. Reggiani 《Cellular and molecular life sciences : CMLS》1972,28(3):307-308
Zusammenfassung Nachweis, dass die Phenethylamin-ausscheidung bei endogener, nicht aber bei sekundär atypischer Depression signifikativ vermindert, bei Manie und Schizophrenie aber entsprechend erhöht ist. Die Behandlung der endogenen, nicht aber der sekundären Depression mit trizyklischen antidepressiven Mitteln erhöht die Phenethylaminausscheidung. Der Phenethylamingehalt im Rattengehirn wird durch Reserpin signifikant vermindert, durch Iproniazid, Imipramin und Chlorimipramin jedoch signifikant erhöht. 相似文献
77.
78.
K. Ostrowski A. Dziedzic-Gocławska J. Michalik W. Stachowicz 《Cellular and molecular life sciences : CMLS》1970,26(8):822-822
Zusammenfassung Das durch die Bestrahlungssterilisation in Knochentransplantaten induzierte stabile ESR-Signal wurde als biologisches Merkmal für die quantitative Bestimmung des zeitlichen Verlaufs der Knochenresorption benützt. Allotransplantate am KaninchenCalvaria ergaben einen linearen Abfall des Spins/mg im Zeitbereich von 0–15 Wochen. 相似文献
79.
A. Popławski 《Cellular and molecular life sciences : CMLS》1970,26(1):86-86
Zusammenfassung Angiotensin erhöht die Plättchen-Aggregation verschiedener aktueller Stoffe. 相似文献
80.
Heilig R Eckenberg R Petit JL Fonknechten N Da Silva C Cattolico L Levy M Barbe V de Berardinis V Ureta-Vidal A Pelletier E Vico V Anthouard V Rowen L Madan A Qin S Sun H Du H Pepin K Artiguenave F Robert C Cruaud C Brüls T Jaillon O Friedlander L Samson G Brottier P Cure S Ségurens B Anière F Samain S Crespeau H Abbasi N Aiach N Boscus D Dickhoff R Dors M Dubois I Friedman C Gouyvenoux M James R Madan A Mairey-Estrada B Mangenot S Martins N Ménard M Oztas S Ratcliffe A Shaffer T Trask B 《Nature》2003,421(6923):601-607
Chromosome 14 is one of five acrocentric chromosomes in the human genome. These chromosomes are characterized by a heterochromatic short arm that contains essentially ribosomal RNA genes, and a euchromatic long arm in which most, if not all, of the protein-coding genes are located. The finished sequence of human chromosome 14 comprises 87,410,661 base pairs, representing 100% of its euchromatic portion, in a single continuous segment covering the entire long arm with no gaps. Two loci of crucial importance for the immune system, as well as more than 60 disease genes, have been localized so far on chromosome 14. We identified 1,050 genes and gene fragments, and 393 pseudogenes. On the basis of comparisons with other vertebrate genomes, we estimate that more than 96% of the chromosome 14 genes have been annotated. From an analysis of the CpG island occurrences, we estimate that 70% of these annotated genes are complete at their 5' end. 相似文献