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11.
12.
The interaction in vitro of the intermediate filament protein vimentin with naturally occurring RNAs and DNAs 总被引:6,自引:0,他引:6
The binding of the intermediate filament protein vimentin to a variety of naturally occurring RNAs and DNAs was studied. The relative capacities of the various nucleic acids to associate with pure [3H]vimentin were determined in competition experiments with 28 S rRNA from Ehrlich ascites tumor cells. The reaction products were analyzed by sucrose gradient centrifugation at low ionic strength and in the presence of EDTA. Under these ionic conditions, vimentin reacted preferentially with single-stranded nucleic acids, particularly with those of high (G + C) content. The vimentin binding potentials of single-stranded RNAs and DNAs were largely comparable. However, when the concentrations of mono- and divalent cations were raised to physiological and higher values, only single-stranded DNA retained its vimentin binding capacity. With increasing KCl concentrations at 0 to 1 mM Mg2+, increasing amounts of vimentin were detected in complexes which sedimented considerably faster than the bulk of the DNA, suggesting cooperative binding of vimentin. The salt optimum of this cooperativity was at 200 mM KCl. Thus, the capability of vimentin to discriminate between single-stranded RNA and DNA under physiological ionic conditions points to specificity of the interaction of vimentin with nucleic acids. 相似文献
13.
Interpretation of Diffusion Susceptibility Data Obtained with 50-μg Carbenicillin Discs Against Gram-Negative Organisms 下载免费PDF全文
A total of 284 clinical isolates of various species of Enterobacteriaceae, Pseudomonas aeruginosa, P. maltophilia, and Acinetobacter anitratum were tested for susceptibility to carbenicillin by the standardized Bauer-Kirby disc diffusion technique and a microtiter broth dilution method. The data obtained led to the following proposed criteria for the interpretation of the results of disc susceptibility tests. Enterobacteriaceae that yield zones of inhibition equal to or greater than 20 mm in diameter around 50-mug discs of carbenicillin are designated as sensitive to the drug; isolates that yield zones measuring from 18 to 19 mm in diameter are reported as of equivocal (intermediate) susceptibility to the drug, whereas those enterobacterial isolates that are characterized by zones of inhibition of 17 mm or less in diameter are interpreted as resistant to carbenicillin. Isolates of P. aeruginosa, P. maltophilia, and A. anitratum yielding zones of 14 mm or more in diameter around 50-mug discs of carbenicillin are reported as sensitive, whereas those isolates that are characterized by zones of 13 mm or less in diameter are reported as resistant to this drug. 相似文献
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Summary In contrast to the immense body of evidence supporting the occurrence of intermediate filament (IF) proteins in the animal kingdom, there is only limited information on their distribution in plants. Nevertheless, a number of immunocytochemical and electron microscopical observations indicate that particularly in higher plant cells IFs contribute to the construction of the cyto- and karyoskeleton. Here we show by whole mount electron microscopy of the giant nuclei extruded together with adhering cytoplasm from the rhizoids of some species of the algal order Dasycladales that cytoplasmic 10 nm filament networks also occur in unicellular, mononucleated green organisms of early evolutionary origin. The filament systems were associated with the residual nuclear envelope which consisted of a dense arrangement of pore complexes suspended by a meshwork of short 5 to 6 nm filaments; structurally it was very similar to the nuclear envelopes obtained from mammalian cells. When the Dasycladales nuclei were processed side by side with mouse skin fibroblasts, the algal filament systems were physically almost indistinguishable from the mammalian vimentin filament network. Embedment-free thin sections of rhizoids have not only confirmed the existence of the perinculear 10 nm filaments and their seamless association with the nuclear envelope, but have demonstrated the existence of an extensive intranuclear meshwork of 10 nm filaments. The latter were morphologically indistinguishable from the perinuclear 10 nm filaments and seem to be connected to these via the nuclear envelope to form a continuum. Among a variety of antibodies directed against mammalian IF proteins, only polyclonal anti-mouse lamin B antibodies decorated the cytoplasmic filaments of the Dasycladales cells. Surprisingly, none of the antibodies decorated the thinner filaments of the nuclear envelope, which possibly represent the nuclear lamina. In accord with this observation, one anti-lamin B antibody recognized in Western blot analysis of a urea extract ofAcetabularia acetabulum rhizoids three polypeptides with Mrs of approximately 47,000, 64,000, and 76,000. The proteins did not react with the -IFA antibody. Since the Dasycladales have a fossil record of nearly 600 million years — an extant genus, Acicularia, also investigated here, evolved about 170 million years ago -, the molecular characterization of the subunit proteins of their cytoplasmic filament systems might throw further light on the evolution and biological role of IFs.Dedicated to Professor Sir Henry Harris on the occasion of his 70th birthday 相似文献
17.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
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19.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
20.
Clathrin-associated adaptor proteins - putting it all together 总被引:1,自引:0,他引:1
Traub LM 《Trends in cell biology》1997,7(2):43-46
Adaptors are multifunctional linker proteins that, as a coated vesicle assembles, tether the clathrin lattice to the underlying membrane bud site. Each adaptor is composed of four distinct protein submits, but how these assemble into the functional complex is not clear. Here, some features of the protein sequences are discussed in an attempt to develop a speculative, low-resolution structural model of possible subunit interactions. 相似文献