排序方式: 共有65条查询结果,搜索用时 15 毫秒
1.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
2.
Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells 总被引:4,自引:2,他引:2
下载免费PDF全文
![点击此处可从《The Journal of general physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction. 相似文献
3.
Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans 总被引:13,自引:3,他引:10
Recent studies of mitochondrial DNA (mtDNA) variation in mammals and
Drosophila have shown an excess of amino acid variation within species
(replacement polymorphism) relative to the number of silent and replacement
differences fixed between species. To examine further this pattern of
nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5
genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans.
Of interest are the frequency spectra of silent and replacement
polymorphisms, and potential variation among genes and taxa in the
departures from neutral expectations. The Drosophila ND3 and ND5 data show
no significant excess of replacement polymorphism using the
McDonald-Kreitman test. These data are in contrast to significant
departures from neutrality for the ND3 gene in mammals and other genes in
Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however,
both Drosophila and human mtDNA show very significant excesses of amino
acid polymorphism. Silent polymorphisms at ND5 show a significantly higher
variance in frequency than replacement polymorphisms, and the latter show a
significant skew toward low frequencies (Tajima's D = -1.954). These
patterns are interpreted in light of the nearly neutral theory where mildly
deleterious amino acid haplotypes are observed as ephemeral variants within
species but do not contribute to divergence. The patterns of polymorphism
and divergence at charge-altering amino acid sites are presented for the
Drosophila ND5 gene to examine the evolution of functionally distinct
mutations. Excess charge-altering polymorphism is observed at the carboxyl
terminal and excess charge-altering divergence is detected at the amino
terminal. While the mildly deleterious model fits as a net effect in the
evolution of nonrecombining mitochondrial genomes, these data suggest that
opposing evolutionary pressures may act on different regions of
mitochondrial genes and genomes.
相似文献
4.
DM Woolley 《The Journal of cell biology》1977,75(3):851-865
Motile spermatozoa from the golden hamster have been arrested by rapid freezing and then fixed with glutaraldehyde at low temperature after substitution with ethylene glycol. As far as can be judged, the flagellar waveforms thus stabilized are similar to those seen in living sperm; in contrast, fixation in glutaraldehyde, without prior freezing, induces agonal changes in flagellar conformation. The characteristics waveform after freeze substitution contains three bends. Approx. half of these flagella are entirely planar. The rest are three dimensional, with the third bend displaced in a regular way from the plane containing the proximal two bends. From the geometry of these flagella, it is concluded that the plane of action of a given bending cycle undergoes a clockwise twist (from a forward viewpoint) as the cycle is succeeded by new bending cycles. This "twisted plane" undulation is quite different from helical movement. The twisting seems to occur abruptly, between cycles, as if each bending cycle has a preferred plane of action. The mechanism underlying the twisting is uncertain. However, on the basis of the angular displacements between the preferred planes, and the findings from electron microscopy, the following idea is presented as a working hypothesis: that, if the most proximal plane of bending is topographically determined by peripheral doublet 1, then successive distal planes of action are influenced predominantly by doublets 2, 3, etc., in clockwise sequence. The merits and weaknesses of this hypothesis are discussed. 相似文献
5.
The ITS sequences of Acropora spp. are the shortest so far identified in
any metazoan and are among the shortest seen in eukaryotes; ITS1 was 70-80
bases, and ITS2 was 100-112 bases. The ITS sequences were also highly
variable, but base composition and secondary structure prediction indicate
that divergent sequence variants are unlikely to be pseudogenes. The
pattern of variation was unusual in several other respects: (1) two
distinct ITS2 types were detected in both A. hyacinthus and A. cytherea,
species known to hybridize in vitro with high success rates, and a putative
intermediate ITS2 form was also detected in A. cytherea; (2) A. valida was
found to contain highly (29%) diverged ITS1 variants; and (3) A.
longicyathus contained two distinct 5.8S rDNA types. These data are
consistent with a reticulate evolutionary history for the genus Acropora.
相似文献
6.
Clément Daboné Ralph Buij Adama Oueda Jacques Boko Adjakpa Wendengoudi Guenda Peter DM Weesie 《Ostrich》2019,90(1):53-61
During the last decades, the critically endangered Hooded Vulture Necrosyrtes monachus has strongly declined across its African range. Although direct persecution has been suggested as a major cause of this decline, little is known about the impact of humans on reproductive output in West Africa. We studied the impact of human activities on the reproductive output of Hooded Vultures in the Garango area of Burkina Faso. Twenty and 56 nesting attempts were monitored, respectively, during the breeding season in 2013/14 and 2014/15, to determine reproductive success and identify causes of nest failure. Annual breeding success varied between 0.68 and 0.71 chicks fledged per breeding pair per year and productivity was assessed at 0.57 chicks fledged per territorial pair in 2014/15. The main threats imposed by humans were poaching of eggs, chicks and collection of nest materials, leading to 20% (13 out of 64 breeding attempts) of nest failures over the two years. An additional important reason for nest failure was the pruning and (partial) cutting of nest trees. Despite this high level of human interference, we found that Hooded Vulture nest success increased with proximity to human settlements, probably because breeding vultures benefit from protection by people against persecution and disturbance. 相似文献
7.
Ramirez DM Leppla SH Schneerson R Shiloach J 《Journal of industrial microbiology & biotechnology》2002,28(4):232-238
The protective antigen (PA) is one of the three components of the anthrax toxin. It is a secreted nontoxic protein with a
molecular weight of 83 kDa and is the major component of the currently licensed human vaccine for anthrax. Due to limitations
found in the existing vaccine formulation, it has been proposed that genetically modified PA may be more effective as a vaccine.
The expression and the stability of two recombinant PA (rPA) variants, PA-SNKE-ΔFF-E308D and PA-N657A, were studied. These
proteins were expressed in the nonsporogenic avirulent strain BH445. Initial results indicated that PA-SNKE-ΔFF-E308D, which
lacks two proteolysis-sensitive sites, is more stable than PA-N657A. Process development was conducted to establish an efficient
production and purification process for PA-SNKE-ΔFF-E308D. pH, media composition, growth strategy and protease inhibitors
composition were analyzed. The production process chosen was based on batch growth of B. anthracis using tryptone and yeast extract as the only source of carbon, pH control at 7.5, and antifoam 289. Optimal harvest time
was 14–18 h after inoculation, and EDTA (5 mM) was added upon harvest for proteolysis control. Recovery of the rPA was performed
by expanded-bed adsorption (EBA) on a hydrophobic interaction chromatography (HIC) resin, eliminating the need for centrifugation,
microfiltration and diafiltration. The EBA step was followed by ion exchange and gel filtration. rPA yields before and after
purification were 130 and 90 mg/l, respectively. The purified rPA, without further treatment, treated with small amounts of
formalin or adsorbed on alum, induced, high levels of IgG anti-PA with neutralization activities. Journal of Industrial Microbiology & Biotechnology (2002) 28, 232–238 DOI: 10.1038/sj/jim/7000239
Received 28 August 2001/ Accepted in revised form 20 December 2001 相似文献
8.
Serine 727 phosphorylation and activation of cytosolic phospholipase A2 by MNK1-related protein kinases 总被引:7,自引:0,他引:7
Hefner Y Borsch-Haubold AG Murakami M Wilde JI Pasquet S Schieltz D Ghomashchi F Yates JR Armstrong CG Paterson A Cohen P Fukunaga R Hunter T Kudo I Watson SP Gelb MH 《The Journal of biological chemistry》2000,275(48):37542-37551
We have previously reported that in thrombin-stimulated human platelets, cytosolic phospholipase A(2) (cPLA2) is phosphorylated on Ser-505 by p38 protein kinase and on Ser-727 by an unknown kinase. Pharmacological inhibition of p38 leads to inhibition of cPLA2 phosphorylation at both Ser-505 and Ser-727 suggesting that the kinase responsible for phosphorylation on Ser-727 is activated in a p38-dependent pathway. By using Chinese hamster ovary, HeLa, and HEK293 cells stably transfected with wild type and phosphorylation site mutant forms of cPLA2, we show that phosphorylation of cPLA2 at both Ser-505 and Ser-727 and elevation of Ca(2+) leads to its activation in agonist-stimulated cells. The p38-activated protein kinases MNK1, MSK1, and PRAK1 phosphorylate cPLA2 in vitro uniquely on Ser-727 as shown by mass spectrometry. Furthermore, MNK1 and PRAK1, but not MSK1, is present in platelets and undergo modest activation in response to thrombin. Expression of a dominant negative form of MNK1 in HEK293 cells leads to significant inhibition of cPLA2-mediated arachidonate release. The results suggest that MNK1 or a closely related kinase is responsible for in vivo phosphorylation of cPLA2 on Ser-727. 相似文献
9.
TRAPP, a highly conserved novel complex on the cis-Golgi that mediates vesicle docking and fusion. 总被引:16,自引:0,他引:16
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
M Sacher Y Jiang J Barrowman A Scarpa J Burston L Zhang D Schieltz J R Yates rd H Abeliovich S Ferro-Novick 《The EMBO journal》1998,17(9):2494-2503
We previously identified BET3 by its genetic interactions with BET1, a gene whose SNARE-like product acts in endoplasmic reticulum (ER)-to-Golgi transport. To gain insight into the function of Bet3p, we added three c-myc tags to its C-terminus and immunopurified this protein from a clarified detergent extract. Here we report that Bet3p is a member of a large complex ( approximately 800 kDa) that we call TRAPP (transport protein particle). We propose that TRAPP plays a key role in the targeting and/or fusion of ER-to-Golgi transport vesicles with their acceptor compartment. The localization of Bet3p to the cis-Golgi complex, as well as biochemical studies showing that Bet3p functions on this compartment, support this hypothesis. TRAPP contains at least nine other constituents, five of which have been identified and shown to be highly conserved novel proteins. 相似文献
10.
West R Whitmon J Williamson YM Moura H Nelson M Melnick N Tondella ML Schieltz D Rees J Woolfitt AR Barr JR Ades EW Carlone GM Sampson JS 《Journal of Proteomics》2012,75(6):1966-1972
Mass spectrometry (MS) coupled with 1-D and 2-D electrophoresis can be utilized to detect and identify immunogenic proteins, but these methods are laborious and time-consuming. We describe an alternative, simple, rapid gel-free strategy to identify multiple immunogenic proteins from Bordetella pertussis (Bp). It couples immunoprecipitation to nano liquid chromatography- tandem mass spectrometry (IP-nLC-MS/MS) and is significantly both time- and labor-saving. We developed a gel-free magnetic bead-based immunoprecipitation (IP) method using different NP-40/PBS concentrations in which solubilized proteins of Bp Tohama I membrane fractions were precipitated with polyclonal rabbit anti-Bp whole cell immune sera. Immune complexes were analyzed by MS and Scaffold analysis (> 95% protein identification probability). Total immunoproteins identified were 50, 63 and 49 for 0.90%, 0.45% and 0.22% NP-40/PBS buffer concentrations respectively. Known Bp proteins identified included pertactin, serotype 2 fimbrial subunit and filamentous hemagglutinin. As proof of concept that this gel-free protein immunoprecipitation method enabled the capture of multiple immunogenic proteins, IP samples were also analyzed by SDS-PAGE and immunoblotting. Bypassing gels and subjecting immunoprecipitated proteins directly to MS is a simple and rapid antigen identification method with relatively high throughput. IP-nLC-MS/MS provides a novel alternative approach for current methods used for the identification of immunogenic proteins. 相似文献