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41.
42.
Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands 总被引:2,自引:2,他引:0
Britten CJ; van den Eijnden DH; McDowell W; Kelly VA; Witham SJ; Edbrooke MR; Bird MI; de Vries T; Smithers N 《Glycobiology》1998,8(4):321-327
The alpha3 fucosyltransferase, FucT-VII, is one of the key
glycosyltransferases involved in the biosynthesis of the sialyl Lewis X
(sLex) antigen on human leukocytes. The sialyl Lewis X antigen
(NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential
component of the recruitment of leukocytes to sites of inflammation,
mediating the primary interaction between circulating leukocytes and
activated endothelium. In order to characterize the enzymatic properties of
the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been
expressed in Trichoplusia ni insect cells. The enzyme is capable of
synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from
3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels
of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies
using fucosylated NeuAcalpha(2-3)-(Galbeta(1- 4)GlcNAc)3-Me acceptors
demonstrate that FucT-VII is able to synthesize both di-fucosylated and
tri-fucosylated structures from mono- fucosylated precursors, but
preferentially fucosylates the distal GlcNAc within a polylactosamine
chain. Furthermore, the rate of fucosylation of the internal GlcNAc
residues is reduced once fucose has been added to the distal GlcNAc. These
results indicate that FucT-VII is capable of generating complex selectin
ligands, in vitro , however the order of fucose addition to the lactosamine
chain affects the rate of selectin ligand synthesis.
相似文献
43.
In spite of the increasing application of DNA fingerprinting to natural
populations and to the genetic identification of humans, explicit methods
for estimation of basic population genetic parameters from DNA
fingerprinting data have not been developed. Contributing to this omission
is the inability to determine, for multilocus fingerprinting probes,
relatively important genetic information, such as the number of loci, the
number of alleles, and the distribution of these alleles into specific
loci. One of the most useful genetic parameters that could be derived from
such data would be the average heterozygosity, which has traditionally been
employed to measure the level of genetic variation within populations and
to compare genetic variation among different loci. We derive here explicit
formulas for both the estimation of average heterozygosity at multiple
hypervariable loci and a maximum value for this estimate. These estimates
are based upon the DNA restriction-pattern matrices that are typical for
fingerprinting studies of humans and natural populations. For several
empirical data sets from our laboratory, estimates of average and maximal
heterozygosity are shown to be relatively close to each other. Furthermore,
variances of these statistics based on simulation studies are relatively
small. These observations, as well as consideration of the effect of
missing alleles and alternate numbers of loci, suggest that the average
heterozygosity can be accurately estimated using phenotypic DNA fingerprint
patterns, because this parameter is relatively insensitive to the lack of
certain genetic information.
相似文献
44.
Analysis of transcripts from two families of nomadic DNA 总被引:14,自引:0,他引:14
45.
K Dhileepan Catherine J Lockett Rachel E McFadyen 《Australian Journal of Entomology》2005,44(1):83-88
Abstract The significance of natural enemies in the failure or reduced effectiveness of weed biological control agents remains largely unknown. Larval and pupal parasitism by native insects in the stem-galling moth Epiblema strenuana was studied in north Queensland, 4 (1986–87) and 16 (1998–99) years after its introduction as a biological-control agent for Parthenium hysterophorus . Specific questions answered in this study are: (i) Has parasitism increased over the years?; (ii) Are the levels of parasitism influenced by the host plant phenology?; and (iii) What are the potential implications of current parasitism levels for the effectiveness of E. strenuana ? There was no increase in the parasitoid species assemblage over the years. In 1986–87, Antrocephalus sp. and Bracon sp. were the most predominant species. The combined larval and pupal parasitism was low (2.6%) and there was no seasonal difference in the parasitism levels. In 1998–99 Bracon sp. was the most prevalent species. Parasitism by Bracon sp. in 1998–99 was several times higher (22.9%) than the combined larval and pupal parasitism in 1986–87. However, parasitism by Bracon sp. remained low (6.5–8.2%) at the beginning of the parthenium-growing season, and reached peak levels (49–53%) only at the end of the season. Parasitism by Bracon sp. was also significantly lower in rosettes (7.2%) than in flowering plants (22.8%). Galling can have a negative impact on the weed only when initiated at the rosette stage. In 1998–99 lower levels of parasitism early in the season when most plants are in the rosette stage suggest that the impact of parasitism on the effectiveness of the gall insect may not be significant. 相似文献
46.
Daelemans D Costes SV Cho EH Erwin-Cohen RA Lockett S Pavlakis GN 《The Journal of biological chemistry》2004,279(48):50167-50175
Nuclear export of intron-containing human immunodeficiency virus type 1 RNA is mediated by the viral Rev protein. Rev is a nucleocytoplasmic transport protein that directly binds to its cis-acting Rev-responsive element RNA. Rev function depends on its ability to multimerize. The in vivo dynamics and the subcellular dependence of this process are still largely unexplored. To visualize and quantitatively analyze the mechanism of Rev multimeric assembly in live cells, we used high resolution in vivo fluorescence resonance energy transfer (FRET) and fluorescence recovery after photobleaching. By using two different dynamic FRET approaches (acceptor photobleaching and donor bleaching time measurements), we observed a strong Rev-Rev interaction in the nucleoli of living cells. Most interestingly, we could also detect Rev multimerization in the cytoplasm; however, FRET efficiency in the cytoplasm was significantly lower than in the nucleolus. By using fluorescence recovery after photobleaching, we investigated the mobility of Rev within the nucleolus. Mathematical modeling of the fluorescence recovery after photobleaching recoveries enabled us to extract relative association and dissociation constants and the diffusion coefficient of Rev in the nucleolus. Our results show that Rev multimerizes in the nucleolus of living cells, suggesting an important role of the nucleolus in nucleocytoplasmic transport. 相似文献
47.
Jennings DB Lockett HJ 《American journal of physiology. Regulatory, integrative and comparative physiology》2000,278(5):R1125-R1133
Spontaneously hypertensive rats (SHR) have an activated brain angiotensin system. We hypothesized 1) that ventilation (V) would be greater in conscious SHR than in control Wistar-Kyoto (WKY) rats and 2) that intravenous infusion of the ANG II-receptor blocker saralasin would depress respiration in SHR, but not in WKY. Respiration and oxygen consumption (VO(2)) were measured in conscious aged-matched groups (n = 16) of adult female SHR and WKY. For protocol 1, rats were habituated to a plethysmograph and measurements obtained over 60-75 min. After installation of chronic intravenous catheters, protocol 2 consisted of 30 min of saline infusion ( approximately 14 microliter. kg(-1). min(-1)) followed by 40 min of saralasin (1.3 microgram. kg(-1). min(-1)). V, tidal volume (VT), inspiratory flow [VT/inspiratory time (TI)], breath expiratory time, and VO(2) were higher, and breath TI was lower in "continuously quiet" SHR. In SHR, but not in WKY rats, ANG II-receptor block decreased V, VT, and VT/TI and increased breath TI. During ANG II-receptor block, an average decrease in VO(2) in SHR was not significant. About one-half of the higher V in SHR appears to be accounted for by an ANG II mechanism acting either via peripheral arterial receptors or circumventricular organs. 相似文献
48.
Lieb JD de Solorzano CO Rodriguez EG Jones A Angelo M Lockett S Meyer BJ 《Genetics》2000,156(4):1603-1621
The dosage compensation machinery of Caenorhabditis elegans is targeted specifically to the X chromosomes of hermaphrodites (XX) to reduce gene expression by half. Many of the trans-acting factors that direct the dosage compensation machinery to X have been identified, but none of the proposed cis-acting X chromosome-recognition elements needed to recruit dosage compensation components have been found. To study X chromosome recognition, we explored whether portions of an X chromosome attached to an autosome are competent to bind the C. elegans dosage compensation complex (DCC). To do so, we devised a three-dimensional in situ approach that allowed us to compare the volume, position, and number of chromosomal and subchromosomal bodies bound by the dosage compensation machinery in wild-type XX nuclei and XX nuclei carrying an X duplication. The dosage compensation complex was found to associate with a duplication of the right 30% of X, but the complex did not spread onto adjacent autosomal sequences. This result indicates that all the information required to specify X chromosome identity resides on the duplication and that the dosage compensation machinery can localize to a site distinct from the full-length hermaphrodite X chromosome. In contrast, smaller duplications of other regions of X appeared to not support localization of the DCC. In a separate effort to identify cis-acting X recognition elements, we used a computational approach to analyze genomic DNA sequences for the presence of short motifs that were abundant and overrepresented on X relative to autosomes. Fourteen families of X-enriched motifs were discovered and mapped onto the X chromosome. 相似文献
49.
50.