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91.
M Peris G C Frech A M Simpson F Bringaud E Byrne A Bakker L Simpson 《The EMBO journal》1994,13(7):1664-1672
The molecular mechanism of RNA editing in trypanosomatid mitochondria is an unsolved problem. We show that two classes of ribonucleoprotein complexes exist in a mitochondrial extract from Leishmania tarentolae and appear to be involved in RNA editing. The 'G' class of RNP complexes consists of 170-300 A particles which contain guide RNAs and proteins, show little terminal uridylyl transferase (TUTase) activity and exhibit an in vitro RNA editing-like activity. The 'T' class consists of approximately six RNP complexes, the endogenous RNA of which can be self-labeled with [alpha-32P]UTP. The most abundant T complex, T-IV, is visualized by electron microscopy as 80-140 A particles. This complex exhibits TUTase activity in the native gel and contains guide RNAs. Both G and T complexes are possibly involved with RNA editing in vivo. These results are a starting point for the analysis of the biochemistry of RNA editing. 相似文献
92.
Nicholas A. Ashbaugh Anthony A. Echelle Alice F. Echelle 《Journal of fish biology》1994,45(2):291-302
Starch gel electrophoresis of proteins was used to study geographic variation at 26 gene loci in the Red River pupfish ( Cyprinodon rubrofluviatílís ), a species restricted to west Texas and Oklahoma. Marked differences were detected between populations in the Red and Brazos river drainages, with fixed or nearly fixed differences occurring at five gene loci. In addition, mean heterozygosity was uniformly high for the Red River form ( = 0·076–0·101) while samples of the Brazos River form were genetically depauperate ( =0·00–0·017). Introduced populations in the South Canadian and Colorado river drainages appear to have been derived from the Red River drainage. The presence of alleles diagnostic of the Red and Brazos river forms supports the suggestion from previous work that they may represent cryptic species. Regardless of taxonomy, however, the presence of two genetically distinct forms must be taken into consideration by those concerned with maintenance of biotic diversity. 相似文献
93.
After considering the need for quality control in NAA, the concept of quality in NAA procedures themselves is discussed, and
some important factors identified. Two approaches to improve quality are then described in more detail. The first concerns
the unique ability of NAA using different isotopic reactions and different modes (INAA/RNAA) to provide independent data sets
in the same laboratory, thus allowing internal validation or crosschecking. The second discusses the need for chemical yield
measurements in RNAA and the advantages of the radioisotopic tracer technique. Some recent advances and further possibilities
for this use of tracers are listed. 相似文献
94.
Felicity Z. Watts Neil Butt Philip Layfield Jesse Machuka Julian F. Burke Anthony L. Moore 《Plant molecular biology》1994,26(1):445-451
An Arabidopsis thaliana gene (UBC6) encoding a homologue to ubiquitin-conjugating enzymes has been isolated which is capable of encoding a protein of 183 amino acids of ca. 21 kDa. Northern analysis indicates that the gene is expressed in flowers, seeds and, to a somewhat lesser extent, in 10-day seedlings but not in mature leaves, callus and pre-flowering plants. This pattern of expression is confirmed using transgenic Arabidopsis plants containing a UBC6 promoter-GUS gene fusion construct. These plants displey GUS activity in mature anthers prior to dehiscence, in developing embryos, sepals and the style after pollination. 相似文献
95.
96.
We present the results of a 5-year examination of variation in the stable carbon isotope composition () of three C3 graminoid species from a Sandhills prairie: Agropyron smithii, Carex heliophila and Stipa comata. Although consistent species-specific patterns for mean were seen, there was also significant and substantial among-year and within-season variation in . A smaller contribution to variation in came from topographic variation among sampling sites. Effects of species, year, season and topography contribute to variation in in an additive manner. An association between climate and exists that is consistent with previous work suggesting that reflects the interplay between photosynthetic gas exchange and plant water relations. Within the growing season, the time over which integrates plant response to the environment ranges from days to months. 相似文献
97.
Midura Ronald J.; Salustri Antonietta; Calabro Anthony; Yanagishita Masaki; Hascall Vincent C. 《Glycobiology》1994,4(3):333-342
Recent literature indicates that specific glycosaminoglycanstructures are involved in various biological processes, suchas anticoagulation, growth factor activation and viral infection.The initial step in the structural analysis of glycosaminoglycansis a definitive compositional analysis of its characteristicdisaccharide repeat structures. Current chromatographic or electrophoreticprocedures may have limitations in analysing glycosaminoglycansamples that are in low abundance, contain novel structuresthat need to be further characterized, or are metabolicallylabelled from radioactive precursors as a result of biosyntheticexperiments. This study presents a new methodology for analysingdisaccharides and oligosaccharides derived from chondroitinsulphate, dermatan sulphate and hyaluronan that fulfils theabove criteria. The procedure involves the separation of reducedforms of these glycoconjugates on a CarboPac PA1 column usingalkaline eluants. This study adopted a strategy which uses specificenzymes to release these disaccharides from their glycosaminoglycanforms. A borohydride reduction reaction was modified to be compatiblewith the buffer conditions commonly used with these enzymesin order to quantitatively reduce the disaccharides to theiralditol forms (thereby stabilizing them to alkaline pH). Chromatographyconditions were established which separated all known disaccharidealditol structures from chondroitin sulphate, dermatan sulphateand hyaluronan with extremely high resolution in a single run.Integrated pulsed amperometry was compared to UV absorbancemeasurement at 232 nm as two sensitive methods for detectingthese reduced disaccharides; most of them could be routinelydetected in the range of 50500 ng. Data are presentedapplying this method to quantify hyaluronan in a biologicalsample which contains {small tilde}5000 cells and only {smalltilde}10 ng of hyaluronan. Additional data are presented todemonstrate that this procedure will also separate oligosaccharidealditols derived from hyaluronan. borohydride reduction glycosaminoglycans integrated pulsed amperometry 相似文献
98.
Anthony P. Fordham-Skelton F. Safadi M. Golovkin A. S. N. Reddy 《Plant Molecular Biology Reporter》1994,12(4):358-366
Calmodulin labeled with125I or34S has been used to screen expression libraries to isolate cDNAs encoding calmodulin-binding proteins (CBPs) from several eukaryotic
systems. The use of radiolabeled calmodulin has, however, several disadvantages. We have developed a nonradiactive method
to isolate cDNAs for CBPs using biotinylated calmodulin. Screening of a cDNA library in an expression vector with biotinylated
calmodulin resulted in the isolation of cDNAs encoding CBPs. Avidin and biotin blocking steps, prior to incubation of the
filters with biotinylated calmodulin, are found to be essential to eliminate the cDNAs that code for biotin-containing polypeptides.
The cDNA clones isolated using this nonradioactive method bound calmodulin in a calcium-dependent manner. The binding of biotinylated
calmodulin to these clones was completely abolished by ethylene glycolbis(\-aminoethylether)-N,N′-tetraacetic acid (EGTA),
a calcium chelator. Furthermore, the isolated cDNAs were confirmed by probing the clones with35S-labeled calmodulin. All the isolated clones bound to radiolabeled calmodulin in the presence of calcium but not in the presence
of EGTA. The method described here is simple, fast, and does not involve preparation and handing of radiolabeled calmodulin.
All the materials used in this method are commercially available; hence, this procedure should be widely applicable to isolate
cDNAs encoding CBPs from any eukaryotic organism. 相似文献
99.
Metallothionein (MT) is a ubiquitous mammalian protein comprising 61 or 62 nonaromatic amino acids of which 20 are cysteine residues. The high sulfhydryl content imparts to this protein a unique and remarkable ability to bind multiple metal ions in structurally significant metal–thiolate clusters. MT can bind seven divalent metal ions per protein molecule in two domains with exclusive tetrahedral metal coordination. The domain stoichiometries for the M7S20 structure are M4(Scys)11 (α domain) and M3(Scys)9 (β domain). Up to 12 Cu(I) ions can displace the 7 Zn2+ ions bound per molecule in Zn7–MT. The incoming Cu(I) ions adopt a trigonal planar geometry with domain stoichiometries for the Cu12S20 structure of Cu6(Scys)11 and Cu6(Scys)9 for the α and β domains, respectively. The circular dichroism (CD) spectra recorded as Cu+ is added to Zn7–MT to form Cu12–MT directly report structural changes that take place in the metal binding region. The spectrum arises under charge transfer transitions between the cysteine S and the Cu(I); because the Cu(I)–thiolate cluster units are located within the chiral binding site, intensities in the CD spectrum are directly related to changes in the binding site. The CD technique clearly indicates stoichiometries of several Cu(I)–MT species. Model Cu(I)–thiolate complexes, using the tripeptide glutathione as the sulfhydryl source, were examined by CD spectroscopy to obtain transition energies and the Cu(I)–thiolate coordination geometries which correspond to these bands. Possible structures for the Cu(I)–thiolate clusters in the α and β domains of Cu12–MT are proposed. © 1994 Wiley-Liss, Inc. 相似文献
100.
Anthony T.W. Cheung Richard B. Moss Geoffrey Kurland Albin B. Leong William J. Novick 《Journal of medical primatology》1993,22(4):257-262
We have recently established a rhesus monkey model of chronic Pseudomonas aeruginosa (PA) endobronchitis by bronchoscopic instillation of PA-embedded agar beads. All experimental animals developed chronic neutrophilic endobronchitis similar to chronic PA endobronchitis in cystic fibrosis (CF). Histopathologic studies further confirmed similarities to chronic PA endobronchitis in CF, including marked peribronchial inflammation, epithelial damage, presence of degraded cilia and ciliary abnormalities, appearance of PA bacterial clusters, mucosal hyperplasia, goblet cell hypertrophy/hypersecretion, airway obstruction, alveolar abnormalities, bronchiectasis, and fibrosis. 相似文献