共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
(AGCTG) (AGCTG) (AGCTG) (GGGTG) as the primordial sequence of intergenic spacers: the role in immunoglobulin class switch 总被引:5,自引:0,他引:5
S Ohno 《Differentiation; research in biological diversity》1981,18(2):65-74
The means employed for immunoglobulin heavy chain class switch appears to be no different from that by which meiotic intergenic crossing-overs at accomplished. As with other intergenic spacers, the 5' noncoding sequence of each Ig CH (immunoglobulin heavy chain constant region) gene apparently undergoes unconstrained sequence changes due to randomly sustained base substitutions, deletions, and duplications. Yet, there remains sufficient regional sequence homology between the Ig Cmu 5' noncoding sequence and those of its somatic recombination partners, e.g., Ig C gamma 1, Ig C gamma 2b, Ig C alpha, because each of these 5' noncoding sequences is made of multiple copies in various stages of degeneracy of one primordial 20 base pair-long sequence: (AGCTG) (AGCTG) (AGCTG) (GGGTG). 相似文献
3.
天然型与非天然型脱落酸的生物活性比较 总被引:2,自引:0,他引:2
采用新方法精制脱落酸(ABA)异构体试样,提高了(S)-(+)-ABA与(R)-(-)-ABA两对映体纯度。抑制生长试验和残留量分析以及气孔闭合试验表明:天然型(S)-(+)-ABA活性显著高于非天然型(R)-(-)-ABA或(SR)-(±)-ABA。抑制莴苣种子发芽50%的活性强度,(S)-(+)-ABA约是(R)-(-)-ABA的5倍,(SR)-(±)-ABA介于两者之间。抑制萝卜下胚轴生长试验,最显著有效期为2~6d,生理作用期约为一周,(S)-(+)-ABA活性是(R)-(一)-ABA的3.5倍。鸭跖革气孔闭合试验,(S)-(+)-ABA活性比(R)-(-)-ABA高1倍。 相似文献
4.
Cytokinesis in bacteria is mediated by a macromolecular machine known as the divisome, consisting of an assembly of FtsZ polymers around the cylindrical axis of the cell and the downstream regulators of division that are subsequently recruited to it. FtsZ polymerizes into filaments in a GTP-dependent manner, similarly to its eukaryotic structural homolog tubulin. The initial placement of the FtsZ polymerization site is tightly regulated by multiple mechanisms, as are the subsequent polymer reshaping and force generation that separate the two daughter cells from each other. New factors have been recently discovered that contribute to this regulation, notably affecting FtsZ polymer shaping, and modulating FtsZ polymerization in response to the metabolic or redox state of the cell. 相似文献
5.
Nobumitsu Kawakubo 《Journal of plant research》1990,103(1):57-66
The morphology and function of the flowers of three species of the genusCallicarpa, C. glabra, C. nisnimurae andC. subpubescens, endemic to the Bonin Islands, revealed that all three species were dioecious. Male plants had short-styled flowers with
sterile ovaries, while female plants had long-styled flowers with non-germinating inaperturate pollen grains. Such dioecism
has never been reported from the family Verbenaceae. This curious sexual system with non-germinating pollen grains may have
been maintained as a reward to insect pollinators. 相似文献
6.
Sandro Lanfranco Christine De Walsche Patrick Schembri Johan Mertens 《Hydrobiologia》1991,212(1):241-243
Four branchiopod species occur on the Maltese Islands, viz. Branchipus schaefferi, B. visnyai, Cyzicus tetracerus and Triops cancriformis. All four live in freshwater pools, but it is noteworthy that, beside B. schaefferi, T. cancriformis was recorded from a mesohaline, coast-fringing habitat. 相似文献
7.
A. P. Rasnitsyn 《Paleontological Journal》2007,41(3):341-344
Alternative current approaches to homology and nomenclature of the insect wing venation are discussed. The differences between the opposing viewpoints are found to be not as deep as they have sometimes been supposed to be, and more so, there are some observations that could help to smooth current contradictions. However, this requires an understanding of the evidence presented by the disputants and, particularly, an understanding of their terminology. 相似文献
8.
N. A. Petrova S. V. Zhirov N. I. Zelentsov E. A. Kachvoryan 《Entomological Review》2011,91(3):360-366
A faunistic review of larvae and pupae of chironomid midges (Diptera, Chironomidae) from 15 habitats in the Hrazdan River
valley (Armenia) is presented. The revealed fauna includes 40 species from 20 genera and 6 families and tribes. Diploid chromosome
numbers are specified for 24 species from 13 genera and 4 subfamilies; 23 species from 14 genera and 4 subfamilies are reported
from the region for the first time. Predominant oligotrophic status is confirmed for most of the reservoirs studied. 相似文献
9.
Immunohistochemical localization of sulfhydryloxidase (SOx) has been examined in the testis of the Axolotl (Ambystoma mexicanum). The urodelan testis contains germ cells in various phases of differentiation from primordial germ cells to mature spermatozoa. SOx immunoreactivity is present in mitochondria of primordial germ cells and primary spermatogonia and declines within the population of secondary spermatogonia, suggesting, that the antibody used to localize SOx may serve to estimate the developmental stage of spermatogonia towards meiosis, since more undifferentiated cells react positively. Intensity of immunostaining increases again in spermatocytes and becomes most intense in early round spermatids correlating on ultrastructural level with an accumulation of numerous mitochondria in that part of the cytoplasm, where the acrosome vesicle is formed. Mature sperm are immunonegative. Additionally, Leydig cells within the glandular tissue are stained by the antibody. Thus the distribution pattern of SOx immunoreactivity principally resembles that in the mammalian testis found during ontogenesis or in the adult seminiferous epithelium. The possible functional significance of mitochondrial SOx in germ cells and Leydig cells is discussed. These results suggest, that the amphibian testis is a model for experimental problems dealing with the investigation of germ cells in various developmental phases including very undifferentiated premeiotic germ cells. The cystic testis may be of value in studying influences of various experimental conditions on varied homogeneous populations of germ cells. 相似文献
10.
Iu B Lishmanov L N Maslov M I Titov 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(9):268-270
It has been shown that the stable analog of leu-enkephalin diminishes to a great extent the stress-induced changes in the blood content of ACTH, cortisol, hypophyseal-thyroid hormones, the CAMP level in the adrenal and thymic tissues of white rats. It is assumed that this circumstance may interfere with depletion of the adrenal cortex and suppression of the lymphoid-macrophagal system. 相似文献
11.
12.
Thirty-eight dugong (Dugong dugon) hearts and 28 Florida manatee (Trichechus manatus) hearts were obtained from stranding programs in Australia and the United States. In addition to a double ventricular apex, a feature that has astonished scientists since the eighteenth century, the hearts of both animals have a double subvalvular conus and a dorsal left atrium. The heart lies in a vertical plane at right angles to that of the completely dorsal, symmetrical lungs. The dugong heart has a deeper interventricular cleft and a more conical left ventricle. The latter features may be part of a general morphological trend toward specialization for a more energetic aquatic existence. The presence of a bulbous ascending aorta in the manatee but not in the dugong is without explanation. 相似文献
13.
Summary A locus, LP, that determines quantitative variation of Lp(a) lipoprotein phenotypes is linked to the plasminogen (PLG) locus (peak lod score =12.73). This linkage relationship assigns a locus with alleles that have an affect on risk for coronary artery disease to the long arm of chromosome 6. 相似文献
14.
Entomological Review - The type and other extensive material of Coprophilus (Zonyptilus) pennifer (Motschulsky, 1845) and some of its synonyms was examined. Coprophilus (Zonyptilus) marginalis... 相似文献
15.
16.
17.
The localization of Mn(2+) in A-tract DNA has been studied by (1)H NMR spectroscopy using a series of self-complementary dodecamer oligonucleotides that contain the sequence motifs A(n)(n) and T(n)A(n), where n = 2, 3, or 4. Mn(2+) localization in the minor groove is observed for all the sequences that have been studied, with the position and degree of localization being highly sequence-dependent. The site most favored for Mn(2+) localization in the minor groove is near the 5'-most ApA step for both the T(n)A(n) and the A(n)T(n) series. For the T(n)A(n) series, this results in two closely spaced symmetry-related Mn(2+) localization sites near the center of each duplex, while for the A(n)T(n) series, the two symmetry-related sites are separated by as much as one half-helical turn. The degree of Mn(2+) localization in the minor groove of the T(n)A(n) series decreases substantially as the AT sequence element is shortened from T(4)A(4) to T(2)A(2). The A(n)T(n) series also exhibits length-dependent Mn(2+) localization; however, the degree of minor groove occupancy by Mn(2+) is significantly less than that observed for the T(n)A(n) series. For both A(n)T(n) and T(n)A(n) sequences, the 3'-most AH2 resonance is the least broadened of the AH2 resonances. This is consistent with the observation that the minor groove of A-tract DNA narrows in the 5' to 3' direction, apparently becoming too narrow after two base pairs for the entry of a fully hydrated divalent cation. The results that are reported illustrate the delicate interplay that exists between DNA nucleotide sequence, minor groove width, and divalent cation localization. The proposed role of cation localization in helical axis bending by A-tracts is also discussed. 相似文献
18.
Wierzbicka-Patynowski I Niewiarowski S Marcinkiewicz C Calvete JJ Marcinkiewicz MM McLane MA 《The Journal of biological chemistry》1999,274(53):37809-37814
There are key differences between the amino acid residues of the RGD loops and the C termini of echistatin, a potent antagonist of alpha(IIb)beta(3), alpha(v)beta(3) and alpha(5)beta(1), and eristostatin, a similar disintegrin selectively inhibiting alpha(IIb)beta(3). In order to identify echistatin motifs required for selective recognition of alpha(v)beta(3) and alpha(5)beta(1) integrins, we expressed recombinant echistatin, eristostatin, and 15 hybrid molecules. We tested them for their ability to inhibit adhesion of different cell lines to fibronectin and von Willebrand factor and to express ligand-induced binding site epitope. The results showed that Asp(27) and Met(28) support recognition of both alpha(v)beta(3) and alpha(5)beta(1). Replacement of Met(28) with Asn completely abolished echistatin's ability to recognize each of the integrins, while replacement of Met(28) with Leu selectively decreased echistatin's ability to recognize alpha(5)beta(1) only. Eristostatin in which C-terminal WNG sequence was substituted with HKGPAT exhibited new activity with alpha(5)beta(1), which was 10-20-fold higher than that of wild type eristostatin. A hypothesis is proposed that the C terminus of echistatin interacts with separate sites on beta(1) and beta(3) integrin molecules. 相似文献
19.
Sven Dänicke Hana Valenta Martin Ganter Bianca Brosig Susanne Kersten Anne-Kathrin Diesing Stefan Kahlert Patricia Panther Jeannette Kluess Hermann-Josef Rothkötter 《Mycotoxin Research》2014,30(3):161-170
Pigs might be exposed to lipopolysaccharides (LPS) and deoxynivalenol (DON) at the same time, and both toxins are thought to interactively affect the intestinal barrier, the innate immune system, and the xenobiotics metabolism. Hence, we aimed at examining the single and combined effects of both toxins on nutrient digestibility and DON metabolism. For this purpose, barrows (26?±?4 kg) were fed restrictedly either a control diet (CON) or a diet contaminated with 3.1 mg DON/kg (DON) for 37 days. At day 37 of the experiment, pigs were infused intravenously for 60 min either with 100 μg DON/kg body weight (BW) (CON-DON), 7.5 μg LPS/kg BW (CON-LPS, DON-LPS) or a combination of both substances (CON-DON?+?LPS), or physiological saline (CON-CON, DON-CON). Blood samples were collected frequently until 3.25 h before the pigs were sacrificed for bile, liver, and kidney collection. The apparent digestibility of N-free extractives was significantly increased by 1 % when the DON-contaminated diet was fed. The total DON content in blood was significantly higher in endotoxemic pigs (34.8 ng/mL; CON-DON?+?LPS) when compared to the pigs infused with DON alone (18.8 ng/mL; CON-DON) while bile concentrations were not influenced by LPS. DON residue levels in liver and kidney closely reflected the treatment effects as described for blood. In contrast to DON infusion, the LPS challenge resulted in a significantly lower total DON concentration (13.2 vs. 7.5 ng/mL in groups DON-CON and DON-LPS, respectively) when the pigs were exposed to DON through the diet. The conjugation degree for DON in blood and bile was not influenced by treatments. In conclusion, endotoxemic pigs are characterized by higher DON residue levels in blood, liver, and kidney, probably by a compromised elimination. 相似文献
20.
讨论了Clematis eriopoda Maxim.和sect.Atragenopsis Boiss.的地位,认为这二分类群均应成立;描述了2新种,1新变种;过去长期被归并的卷萼铁线莲C.tubulosa得到恢复;Clematisheracleifoliavar.ichangensis被转移改作卷萼铁线莲的变种;首次给出光叶铁线莲Clematisglabrifolia的果实的形态描述。 相似文献