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991.
992.
Hubert H. Felle Éva Kondorosi Ádám Kondorosi Michael Schultze 《The Plant journal : for cell and molecular biology》1995,7(6):939-947
Lipochitooligosaccharide Nod signals are important determinants of host specificity in the Rhizobium -legume symbiosis. The most rapid response of plant cells to the R. meliloti Nod signal NodRm-IV(C16:2,S) reported so far is the depolarization of the plasma membrane potential in alfalfa root hairs. In order to investigate whether this response may be part of a specific signal transduction cascade involved in the nodulation process, its specificity was studied with respect to host-specific modifications of the lipochitooligosaccharide. Five different Nod factors displaying different degrees of activity in inducing root hair deformation or cortical cell divisions on alfalfa were tested. The ability of the Nod factors to elicit plasma membrane depolarization correlated well with their activity in the bioassays. Removal of the sulfate group (NodRm-IV(C16:2)) led to inactivation of the Nod factor. An increase in the length of the chitooligosaccharide backbone (NodRm-V(C16:2,S)) or saturation of the acyl chain (NodRm-IV(C16:0,S)) resulted in severely reduced activity. In contrast, the O -acetyl group at the non-reducing terminus in NodRm-IV(Ac,C16:2,S), which confers substantially higher activity in long-term bioassays, did not enhance plasma membrane depolarization significantly in comparison with the non- O -acetylated factor. Thus, the rapid plasma membrane response is differentially sensitive to various structural motifs of the lipochitooligosaccharide. These data suggest that the different substituents modifying the basic Nod factor structure may have distinct functions, not all of them contributing to the interaction with a putative receptor in root hair cells. However, the overall specificity of the membrane depolarization for the cognate Nod factors raises the possibility that it is involved in a Nod signal transduction pathway. 相似文献
993.
The calcium hypothesis of cystic fibrosis 总被引:1,自引:0,他引:1
Data have been presented which suggests that various CF cell types show evidence of alterations in calcium homeostasis. The significance of these observations and the exact nature of the putative calcium defect in CF remains to be elucidated. It must also be determined whether this possible defect is primary, or is secondary or tertiary to some more basic lesion. The data reviewed suggests that altered calcium homeostasis may play some focal role in the aetiology or the pathogenesis of CF. 相似文献
994.
cDNA clones of human complement components C4A and C4B alleles were prepared from mRNA obtained from the liver of a donor heterozygous at both loci. cDNA from one C4A allele was sequenced to give the derived complete amino acid sequence of 1722 amino acid residues of the C4 single chain precursor molecule and the estimated sequences of the three peptide chains of secreted C4. Comparison with partial sequences of a second C4A allele and a C4B allele has led to the tentative identification of some class differences in nucleotide sequences between C4A and C4B and of allelic differences between C4A alleles in this highly polymorphic system. 相似文献
995.
Human β-globin mRNA precursors (pre-mRNAs) synthesized in vitro from a bacteriophage SP6 promoter/β-globin gene fusion are accurately and efficiently spliced when added to a HeLa cell nuclear extract. Under optimal conditions, the first intervening sequence (IVS 1) is removed by splicing in up to 90% of the input. pre-mRNA. Splicing requires ATP and in its absence the pre-mRNA is neither spliced nor cleaved at splice junctions. Splicing does not require that the pre-mRNA contain a correct 5′ or 3′ end, a 3′ poly A tail, or a 5′-terminal cap structure. However, capping of the pre-mRNA significantly affects the specificity of in vitro processing. In the absence of a cap approximately 30%–40% of the pre-mRNA is accurately spliced, and a number of aberrantly cleaved RNAs are also detected. In contrast, capped pre-mRNAs are spliced more efficiently and produce fewer aberrant RNA species. The specificity of splice-site selection in vitro was tested by analyzing pre-mRNAs that contain β-thalassemia splicing mutations in IVS 1. Remarkably, these mutations cause the same abnormal splicing events in vitro and in vivo. The ability to synthesize mutant pre-mRNAs and study their splicing in a faithful in vitro system provides a powerful approach to determine the mechanisms of RNA splice-site selection. 相似文献
996.
Joseph R. Lacy Christopher M. Filley Michael P. Earnest Neill R. Graff-Radford 《The Western journal of medicine》1984,141(3):329-334
Of 131 young (17 to 44 years) and middle-aged (45 to 55 years) adults who had brain infarction or hemorrhage, the most common etiologic factors were rheumatic heart disease, migraine and oral contraceptive use among the younger group. In contrast, atherosclerotic, hypertensive and diabetes-associated cerebrovascular were the most common causes in the middle-aged group. Patients who have a stroke before age 45 should have prompt, complete laboratory and radiologic testing to define a possible treatable cause. 相似文献
997.
Peter J. Robinson Michael Steinmetz Kazuo Moriwaki Kirsten Fischer Lindahl 《Immunogenetics》1984,20(6):655-665
To determine the distribution of beta-2 microglobulin (B2m) alleles in wild mice we have typed mice derived from natural populations in Europe, North Africa, South America, and East Asia. Mus musculus domesticus mice from Germany, France, Italy, and Peru were all B2m
a
as were most from the United Kingdom. M.m. musculus mice from Denmark and Czechoslovakia, several stocks of M.m. molossinus from Japan, and M.m. castaneus from China, Thailand, and the Philippines were of B2m
b
type. This is consistent with the notion that C57BL/6 may have obtained some of its genes, including B2m, from Eastern mice. A BgII restriction site characteristic of B2m
b
was also found in mice from Czechoslovakia and Japan, confirming that B2m
b
is a naturally occurring allele of B2m. A new type of
2m (
2mw1) was found in four stocks of M. spretus from Portugal, Spain, and Morocco. This molecule differs in apparent size and charge from the a and b types.
2mw2 was found together with
2 ma in one stock of M.m. domesticus (brevirostris) from Morocco.
2mw3 and
2mw4 were found in a few M. m. bactrianus from Pakistan. In all cases tested, these new
2m molecules associate with class I histocompatibility antigens.Abbreviations used in this paper
2m
beta-2 microglobulin
-
B2m
gene for beta-2 microglobulin
- IEF
isoelectric focusing
- SDS-PAGE
polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate
- MHC
major histocompatibility complex
- T. E.
Tris-EDTA buffer 相似文献
998.
Michael D. Papagiannis 《Origins of life and evolution of the biosphere》1984,14(1-4):43-50
It is generally thought that the Universe started with a big explosion (Big Bang) approximately 15 billion years ago. Hydrogen and helium were formed within the first few minutes, while all the other chemical elements are the by-products of stellar evolution that are added to the interstellar medium through the supernova explosions of the larger stars. Carbon, Oxygen, Hydrogen and Nitrogen, which constitute about 98% of the biomass of the Earth, are also among the most abundant chemical elements in the Universe. A seemingly unique combination of the fundamental laws and constants of the Universe made possible the origin and subsequent slow evolution of life. 相似文献
999.
Clostridium thermocellum: Adhesion and sporulation while adhered to cellulose and hemicellulose 总被引:1,自引:0,他引:1
Summary During growth in the presence of fibers composed of cellulose or hemicellulose, various strains of the thermophilic soil bacterium Clostridium thermocellum and several newly isolated thermophilic anaerobic soil bacteria adhered to the fibers. Attachment occurred via a fibrous ruthenium red-staining material. C. thermocellum sporulated while attached to the fibers when the pH dropped below 6.4. It is postulated that the attachment is involved in cellulose breakdown and that C. thermocellum gaines an advantage by remaining attached to its insoluble substrates when the environment is not suitable for rapid growth. The tendency to adhere to cellulose fibers was used in the purification of thermophilic cellulolytic anaerobes. 相似文献
1000.
Michael J. Hall Louis J. Nisbet Donald Westmacott Philippe Wong-Kai-In 《Journal of microbiological methods》1984,2(4):203-214
Roche Susceptibility Test (RST) Medium represents the most completely optimized and convenient fully defined medium described. It requires no post-autoclaving supplementation with vitamins, supports good growth of all common aerobic and anaerobic pathogens and may be used as a broth or agar gel on which the swarming of Proteus spp. is virtually eliminated. The broth as a superior buffering capacity to most complex media and an osmolality and pH close to those of human serum. RST is highly satisfactory for the susceptibility testing of commonly used antibiotics and meets the requirements of the National Committe for Clinical Laboratory Standards of the U.S.A. in almost every respect. 相似文献