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1.
An understanding of the mechanisms of phytoplankton species interaction is dependent on a precise knowledge of what species exist within the community. The centric diatoms of Lake Tahoe, California-Nevada, which are often the dominant component of the phytoplankton community, are presented in both light and scanning electron microscopy (SEM) photographs. Specific attention has been given to initial cell forms of Cyclotella stelligera Cleve and Grunow and C. comta (Ehrenberg) Kützing through the aid of the SEM. 相似文献
2.
Binding of the antiprotease Trasylol to human peripheral blood lymphocytes and polymorphonuclear leucocytes (PMNs) was demonstrated at the ultrastructural level using an indirect immunoperoxidase technique. This also revealed endocytosis of membrane bound Trasylol by PMNs. Trasylol inhibited PHA- and ConA-induced lymphocyte stimulation, and was cytotoxic to unstimulated cells. 相似文献
3.
4.
Morelli G Song Y Mazzoni CJ Eppinger M Roumagnac P Wagner DM Feldkamp M Kusecek B Vogler AJ Li Y Cui Y Thomson NR Jombart T Leblois R Lichtner P Rahalison L Petersen JM Balloux F Keim P Wirth T Ravel J Yang R Carniel E Achtman M 《Nature genetics》2010,42(12):1140-1143
Plague is a pandemic human invasive disease caused by the bacterial agent Yersinia pestis. We here report a comparison of 17 whole genomes of Y. pestis isolates from global sources. We also screened a global collection of 286 Y. pestis isolates for 933 SNPs using Sequenom MassArray SNP typing. We conducted phylogenetic analyses on this sequence variation dataset, assigned isolates to populations based on maximum parsimony and, from these results, made inferences regarding historical transmission routes. Our phylogenetic analysis suggests that Y. pestis evolved in or near China and spread through multiple radiations to Europe, South America, Africa and Southeast Asia, leading to country-specific lineages that can be traced by lineage-specific SNPs. All 626 current isolates from the United States reflect one radiation, and 82 isolates from Madagascar represent a second radiation. Subsequent local microevolution of Y. pestis is marked by sequential, geographically specific SNPs. 相似文献
5.
Telomere-associated chromosome fragmentation (TACF) is a new approach for chromosome mapping based on the non-targeted introduction of cloned telomeres into mammalian cells. TACF has been used to generate a panel of somatic cell hybrids with nested terminal deletions of the long arm of the human X chromosome, extending from Xq26 to the centromere. This panel has been characterized using a series of X chromosome loci. Recovery of the end clones by plasmid rescue produces a telomeric marker for each cell line and partial sequencing will allow the generation of sequence tagged sites (STSs). TACF provides a powerful and widely applicable method for genome analysis, a general way of manipulating mammalian chromosomes and a first step towards constructing artificial mammalian chromosomes. 相似文献
6.
Bentley SD Chater KF Cerdeño-Tárraga AM Challis GL Thomson NR James KD Harris DE Quail MA Kieser H Harper D Bateman A Brown S Chandra G Chen CW Collins M Cronin A Fraser A Goble A Hidalgo J Hornsby T Howarth S Huang CH Kieser T Larke L Murphy L Oliver K O'Neil S Rabbinowitsch E Rajandream MA Rutherford K Rutter S Seeger K Saunders D Sharp S Squares R Squares S Taylor K Warren T Wietzorrek A Woodward J Barrell BG Parkhill J Hopwood DA 《Nature》2002,417(6885):141-147
Streptomyces coelicolor is a representative of the group of soil-dwelling, filamentous bacteria responsible for producing most natural antibiotics used in human and veterinary medicine. Here we report the 8,667,507 base pair linear chromosome of this organism, containing the largest number of genes so far discovered in a bacterium. The 7,825 predicted genes include more than 20 clusters coding for known or predicted secondary metabolites. The genome contains an unprecedented proportion of regulatory genes, predominantly those likely to be involved in responses to external stimuli and stresses, and many duplicated gene sets that may represent 'tissue-specific' isoforms operating in different phases of colonial development, a unique situation for a bacterium. An ancient synteny was revealed between the central 'core' of the chromosome and the whole chromosome of pathogens Mycobacterium tuberculosis and Corynebacterium diphtheriae. The genome sequence will greatly increase our understanding of microbial life in the soil as well as aiding the generation of new drug candidates by genetic engineering. 相似文献
7.
Perhaps the most enduring of puzzles in palaeontology has been the identity of Palaeospondylus gunni Traquair, a tiny (5-60-mm) vertebrate fossil from the Middle Devonian period (approximately 385 Myr ago) of Scotland, first discovered in 1890 (refs 1-3). It is known principally from a single site (Achanarras Quarry, Caithness) where, paradoxically, it is extremely abundant, preserved in varved lacustrine deposits along with 13 other genera of fishes. Here we show that Palaeospondylus is the larval stage of a lungfish, most probably Dipterus valenciennesi Sedgwick and Murchison 1828 (ref. 5), and that development of the adult form requires a distinct metamorphosis. Palaeospondylus is the oldest known true larva of a vertebrate. 相似文献
8.
Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18. 总被引:33,自引:0,他引:33
J Parkhill G Dougan K D James N R Thomson D Pickard J Wain C Churcher K L Mungall S D Bentley M T Holden M Sebaihia S Baker D Basham K Brooks T Chillingworth P Connerton A Cronin P Davis R M Davies L Dowd N White J Farrar T Feltwell N Hamlin A Haque T T Hien S Holroyd K Jagels A Krogh T S Larsen S Leather S Moule P O'Gaora C Parry M Quail K Rutherford M Simmonds J Skelton K Stevens S Whitehead B G Barrell 《Nature》2001,413(6858):848-852
Salmonella enterica serovar Typhi (S. typhi) is the aetiological agent of typhoid fever, a serious invasive bacterial disease of humans with an annual global burden of approximately 16 million cases, leading to 600,000 fatalities. Many S. enterica serovars actively invade the mucosal surface of the intestine but are normally contained in healthy individuals by the local immune defence mechanisms. However, S. typhi has evolved the ability to spread to the deeper tissues of humans, including liver, spleen and bone marrow. Here we have sequenced the 4,809,037-base pair (bp) genome of a S. typhi (CT18) that is resistant to multiple drugs, revealing the presence of hundreds of insertions and deletions compared with the Escherichia coli genome, ranging in size from single genes to large islands. Notably, the genome sequence identifies over two hundred pseudogenes, several corresponding to genes that are known to contribute to virulence in Salmonella typhimurium. This genetic degradation may contribute to the human-restricted host range for S. typhi. CT18 harbours a 218,150-bp multiple-drug-resistance incH1 plasmid (pHCM1), and a 106,516-bp cryptic plasmid (pHCM2), which shows recent common ancestry with a virulence plasmid of Yersinia pestis. 相似文献
9.
One class of excitatory amino-acid receptors, the N-methyl-D-aspartate (NMDA) receptors, mediates transmission at a small, but important, group of synapses in the neocortex. These receptors are implicated in neuronal plasticity during development in young mammals and in memory acquisition in adults. Recently, responses of isolated membrane patches to NMDA were shown to be greatly enhanced by glycine. This, together with the demonstration that the strychnine-insensitive glycine-binding site is distinct from, but linked to, the NMDA receptor has excited intense interest in glycine as a synaptic modulator. Before proposing a physiological function, however, it is important to determine whether glycine could enhance synaptic responses to NMDA receptor activation in intact, adult tissue. An earlier study failed to demonstrate enhancement of NMDA responses when glycine was applied and it was proposed that in intact tissue the high-affinity glycine site was already saturated by endogenous glycine. It remained possible that glycine concentrations can be maintained at low levels close to synaptic receptors. We have examined responses of neurons in slices of adult neocortex to focal applications of excitatory amino acids and glycine and report enhancement by glycine of NMDA receptor-mediated excitatory postsynaptic potentials. 相似文献
10.
M. N. Galbraith D. H. S. Horn E. J. Middleton J. A. Thomson 《Cellular and molecular life sciences : CMLS》1972,28(3):264-265
Résumé Dans la mouche a viandeCalliphora stygia le 25-hydroxycholesterol et le (22R)-22-hydroxycholesterol sont incorporés a la -ecdysone (20-hydroxy-ecdysone) beaucoup moins qu'au cholesterol et ne sont donc probablement pas des précurseurs de cette hormone. 相似文献