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1.
We have evaluated codon usage bias in Drosophila histone genes and have
obtained the nucleotide sequence of a 5,161-bp D. hydei histone gene repeat
unit. This repeat contains genes for all five histone proteins (H1, H2a,
H2b, H3, and H4) and differs from the previously reported one by a second
EcoRI site. These D. hydei repeats have been aligned to each other and to
the 5.0-kb (i.e., long) and 4.8-kb (i.e., short) histone repeat types from
D. melanogaster. In each species, base composition at synonymous sites is
similar to the average genomic composition and approaches that in the small
intergenic spacers of the histone gene repeats. Accumulation of synonymous
changes at synonymous sites after the species diverged is quite high. Both
of these features are consistent with the relatively low codon usage bias
observed in these genes when compared with other Drosophila genes. Thus,
the generalization that abundantly expressed genes in Drosophila have high
codon bias and low rates of silent substitution does not hold for the
histone genes.
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3.
Epididymal sperm from the painted turtle (Chrysemys picta) possess a cytoplasmic droplet which is located eccentrically on the sperm midpiece. The droplet contains a large quantity of lipid droplets in addition to hollow vesicles and degenerate mitochondrial fragments. Lipid droplets are closely associated with mitochondrial membranes and may function in the formation or degradation of mitochondria. Cytoplasmic droplets become detached from the sperm midpiece in a coordinated manner shortly before the commencement of fall mating and are not observed on sperm recovered from the oviduct of females. © 1992 Wiley-Liss, Inc. 相似文献
4.
Megalin is an endocytic receptor that binds multiple ligands and is essential for many physiological processes such as brain development and uptake of proteins by the kidney tubule, yolk sac, and thyroid. The cytoplasmic tail of megalin contains two FXNPXY motifs. Autosomal recessive hypercholesterolemia (ARH) is an adaptor protein that binds to the FXNPXY motif of the low-density lipoprotein receptor as well as clathrin and AP-2. We found that ARH also binds to the first FXNPXY motif of megalin in two-hybrid, pull-down and coimmunoprecipitation assays. ARH colocalizes with megalin in clathrin coated pits and in recycling endosomes in the Golgi region. When cells are treated with nocodazole, the recycling endosomes containing megalin and ARH disperse. On internalization of megalin, ARH and megalin are first seen in clathrin coated pits followed by sequential localization in early endosomes and tubular recycling endosomes in the pericentriolar region followed by their reappearance at the cell surface. Expression of ARH in Madin-Darby canine kidney cells expressing megalin mini-receptors enhances megalin-mediated uptake of 125I-lactoferrin, a megalin ligand. These results show that ARH facilitates endocytosis of megalin, escorts megalin along its endocytic route and raise the possibility that transport through the endosomal system is selective and requires interaction with specific adaptor proteins. 相似文献
5.
The cytological changes to germ cells were investigated within the seminiferous epithelium of the American alligator (Alligator mississippiensis). Testicular tissues were collected, embedded in plastic, sectioned on an ultramicrotome, and stained with the periodic acid–Schiff+ procedure followed by a haematoxylin counterstain. Alligators have a prenuptial pattern of germ cell development, where spermatogenesis begins in early spring and sperm is mature by the time mating begins in May. Consistent spatial relationships between germ cells are absent within the seminiferous epithelium of the alligator. Their germ cells progress through the phases of spermatogenesis as a single cohort, leading to one continuous spermiation event that occurs during their mating season (May–June). This temporal germ cell development is different from the consistent spatial development seen within seasonally breeding birds and mammals but is similar to the recently described germ cell development strategies of two other temperate breeding reptiles, the slider turtle and the European wall lizard. The germ cell development strategy shared by these three temperate reptiles representing three different taxa within the class Reptilia is reminiscent of the temporal strategy seen within the anamniotic testis. Thus, alligators and at least two other temperate reptiles exhibit primitive spermatogenic cycles within derived amniotic testes and may be consider intermediates in terms of testicular organization, which may have significance phylogenetically. 相似文献
6.
Immunoisolation and Characterization of a Subdomain of the Endoplasmic Reticulum That Concentrates Proteins Involved in COPII Vesicle Biogenesis 总被引:3,自引:2,他引:1
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Tom C. Hobman Baoping Zhao Honey Chan Marilyn Gist Farquhar 《Molecular biology of the cell》1998,9(6):1265-1278
Rubella virus E1 glycoprotein normally complexes with E2 in the endoplasmic reticulum (ER) to form a heterodimer that is transported to and retained in the Golgi complex. In a previous study, we showed that in the absence of E2, unassembled E1 subunits accumulate in a tubular pre-Golgi compartment whose morphology and biochemical properties are distinct from both rough ER and Golgi. We hypothesized that this compartment corresponds to hypertrophied ER exit sites that have expanded in response to overexpression of E1. In the present study we constructed BHK cells stably expressing E1 protein containing a cytoplasmically disposed epitope and isolated the pre-Golgi compartment from these cells by cell fractionation and immunoisolation. Double label indirect immunofluorescence in cells and immunoblotting of immunoisolated tubular networks revealed that proteins involved in formation of ER-derived transport vesicles, namely p58/ERGIC 53, Sec23p, and Sec13p, were concentrated in the E1-containing pre-Golgi compartment. Furthermore, budding structures were evident in these membrane profiles, and a highly abundant but unknown 65-kDa protein was also present. By comparison, marker proteins of the rough ER, Golgi, and COPI vesicles were not enriched in these membranes. These results demonstrate that the composition of the tubular networks corresponds to that expected of ER exit sites. Accordingly, we propose the name SEREC (smooth ER exit compartment) for this structure. 相似文献
7.
Fucose is a major constituent of the protein- and lipid-linked glycans of
the various life-cycle stages of schistosomes. These fucosylated glycans
are highly antigenic and seem to play a role in the pathology of
schistosomiasis. In this article we describe the identification and
characterization of two fucosyltransferases (FucTs) in cercariae of the
avian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Galbeta1--
>4]GlcNAcbeta-R alpha1-->3-FucT and a novel GDP-Fuc:Fucalpha-R
alpha1-- >2-FucT. Triton X-100 extracts of cercariae were assayed for
FucT activity using a variety of acceptor substrates. Type 1 chain
(Galbeta1- ->3GlcNAc) based compounds were poor acceptors, whereas those
based on a type 2 chain (Galbeta1-->4GlcNAc), whether
alpha2'-fucosylated, alpha3'-sialylated, or unsubstituted, and whether
present as oligosaccharide or contained in a glycopeptide or glycoprotein,
all served as acceptor substrates. In this respect the schistosomal alpha3-
FucT resembles human FucT V and VI rather than other known FucTs. N-
ethylmaleimide, an inhibitor of several human FucTs, had no effect on the
activity of the schistosomal alpha3-FucT, whereas GDP-beta-S was strongly
inhibitory. Large scale incubations were carried out with
Galbeta1-->4GlcNAc, GalNAcbeta1-->4GlcNAcbeta-O -(CH2)8COOCH3 and
Fucalpha1-->3GlcNAcbeta1-->2Man as acceptor substrates and the
products of the incubations were isolated using a sequence of
chromatographic techniques. By methylation analysis and 2D-TOCSY and
ROESY1H-NMR spectroscopy the products formed were shown to be Galbeta1--
>4[Fucalpha1-->2Fucalpha1-->3]GlcNAc,
GalNAcbeta1-->4[Fucalpha1-- >2Fucalpha1-->3]GlcNAcbe
ta-O-(CH2)8COOCH3, and Fucalpha1-->2Fucalpha1--
>3GlcNAcbeta1-->2Man, respectively. It is concluded that the alpha2-
FucT and alpha3-FucT are involved in the biosynthesis of the (oligomeric)
Lewisx sequences and the Fucalpha1-->2Fucalpha1-->3GlcNAc structural
element that have been described on schistosomal glycoconjugates.
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8.
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.
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9.
We have identified a novel N -acetylgalactosaminyltransferase activity in
lactating bovine mammary gland membranes. Acceptor specificity studies and
analysis of products obtained in vitro by 400 MHz1H-NMR spectroscopy
revealed that the enzyme catalyses the transfer of N - acetylgalactosamine
(GalNAc) from UDP-GalNAc to acceptor substrates carrying a terminal,
beta-linked N -acetylglucosamine (GlcNAc) residue and establishes a
beta1-->4-linkage forming a GalNAcbeta1-->4GlcNAc ( N, N
'-diacetyllactosediamine, lacdiNAc) unit. Therefore, the enzyme can be
identified as a UDP-GalNAc:GlcNAcbeta-R beta1-->4-N-
acetylgalactosaminyltransferase (beta4-GalNAcT). This enzyme resembles
invertebrate beta4-GalNAcT as well as mammalian beta4-
galactosyltransferase (beta4-GalT) in acceptor specificity. It can,
however, be clearly distinguished from the pituitary hormone-specific
beta4-GalNAcT by its incapability of acting with an elevated activity on a
glycoprotein substrate carrying a hormone-specific peptide motif.
Furthermore, the GalNAcT activity appeared not to be due to a promiscuous
action of a beta4-GalT as could be demonstrated by comparing the
beta4-GalNAcT and beta4-GalT activities of the mammary gland, bovine
colostrum, and purified beta4-GalT, by competition studies with UDP-GalNAc
and UDP-Gal, and by use of an anti-beta4-GalT polyclonal inhibiting
antibody. Interestingly, under conditions where mammalian beta4-GalT forms
with alpha-lactalbumin (alpha-LA) the lactose synthase complex, the mammary
gland beta4-GalNAcT was similarly induced by alpha-LA to act on Glc with an
increased efficiency yielding the lactose analog GalNAcbeta1-->4Glc.
This enzyme thus forms the second example of a mammalian
glycosyltransferase the specificity of which can be modified by this milk
protein. It is proposed that the mammary gland beta4-GalNAcT functions in
the synthesis of lacdiNAc- based, complex-type glycans frequently occurring
on bovine milk glycoproteins. The action of this enzyme is to be considered
when aiming at the production of properly glycosylated protein
biopharmaceuticals in the milk of transgenic dairy animals.
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