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101.
Control of flower development and phyllotaxy by meristem identity genes in antirrhinum. 总被引:9,自引:0,他引:9 下载免费PDF全文
The flower meristem identity genes floricaula (flo) and squamosa (squa) promote a change in phyllotaxy from spiral to whorled in Antirrhinum. To determine how this might be achieved, we have performed a combination of morphological, genetic, and expression analyses. Comparison of the phenotypes and RNA expression patterns of single and double mutants with the wild type showed that flo and squa act together to promote flower development but that flo is epistatic to squa with respect to early effects on phyllotaxy. We propose that a common process underlies the phyllotaxy of wildtype, flo, and squa meristem development but that the relative timing of primordium initiation or growth is altered. This process depends on two separable events: setting aside zones for potential primordium initiation and partitioning these zones into discrete primordia. Failure of the second event can lead to the formation of continuous double spirals, which are occasionally seen in flo mutants. 相似文献
102.
103.
Analysis of HLA and Disease Susceptibility: Chromosome 6 Genes and Sex Influence Long-QT Phenotype 总被引:3,自引:1,他引:2 下载免费PDF全文
Lowell R. Weitkamp Arthur J. Moss Raymond A. Lewis W. J. Hall Jean W. MacCluer Peter J. Schwartz Emanuela H. Locati Dan Tzivoni G. Michael Vincent Jennifer L. Robinson Sally A. Guttormsen 《American journal of human genetics》1994,55(6):1230-1241
The long-QT (LQT) syndrome is a genetically complex disorder that is characterized by syncope and fatal ventricular arrhythmias. LQT syndrome, as defined by a prolonged electrocardiographic QT interval, has a higher incidence in females than in males and does not exhibit Mendelian transmission patterns in all families. Among those families that are nearly consistent with Mendelian transmission, linkage between a locus for LQT syndrome and the H-ras-1 locus on the short arm of chromosome 11 has been reported in some families but not in others. Earlier analyses suggesting that LQT syndrome might be caused by a gene in the HLA region of chromosome 6 were not confirmed by standard linkage analyses. Here, we present an analysis of HLA haplotype sharing among affected pedigree members, showing an excess of haplotype sharing in a previously published Japanese pedigree and possibly also in 15 families of European descent. The haplotypes shared by affected individuals derive from both affected and unaffected parents. In an analysis of independent (unrelated) HLA haplotypes, we also found a nonrandom distribution of HLA-DR genes in LQT syndrome patients compared with controls, suggesting an association between the LQT phenotype and specific HLA-DR genes. Our data indicate that DR2 has a protective effect and, particularly in males, that DR7 may increase susceptibility to the LQT syndrome. Thus, LQT syndrome may be influenced by genes on chromosomes 11 and 6, possibly with a sex-specific effect. These results provide a model for an effect of HLA-region genes inherited from either parent on the expression of an illness that may be determined principally by alleles at loci not linked to HLA. 相似文献
104.
Tova Rahn Martin Ridderstrle Hans Tornqvist Vincent Manganiello Gudrun Fredrikson Per Belfrage Eva Degerman 《FEBS letters》1994,350(2-3):314-318
Incubation of rat adipocytes with wortmannin, a potent and selective phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, completely blocked the antilipolytic action of insulin (IC50≈ 100 nM), the insulin-induced activation and phosphorylation of cGMP-inhibited cAMP phosphodiesterase (cGI-PDE) as well as the activation of the insulin-stimulated cGI-PDE kinase (IC50≈ 10–30 nM). No direct effects of the inhibitor on the insulin-stimulated cGI-PDE kinase, the cGI-PDE and the hormone-sensitive lipase were observed. These data suggest that activation of PI 3-kinase upstream of the insulin-stimulated cGI-PDE kinase in the antilipolytic insulin signalchain has an essential role for insulin-induced cGI-PDE activation/ phosphorylation and anti-lipolysis. 相似文献
105.
106.
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
107.
Abstract Mycobacteria show a high degree of intrinsic resistance to most antibiotics and chemotherapeutic agents. The low permeability of the mycobacterial cell wall, with its unusual structure, is now known to be a major factor in this resistance. Thus hydrophilic agents cross the cell wall slowly because the myobacterial porin is inefficient in allowing the permeation of solutes and exists in low concentration. Lipophilic agents are presumably slowed down by the lipid bilayer which is of unusually low fluidity and abnormal thickness. Nevertheless, the cell wall barrier alone cannot produce significant levels of drug resistance, which requires synergistic contribution from a second factor, such as the enzymatic inactivation of drugs. 相似文献
108.
M. C. Press A. N. Parsons A. W. Mackay C. A. Vincent V. Cochrane W. E. Seel 《Oecologia》1993,95(1):145-151
Plant height, light-saturated rates of photosynthesis (A
max) and foliar nitrogen concentration (N
1) were measured forBartsia trixago under field conditions in Mallorca. All three variables were postively correlated, and were also positively related to the abundance of nitrogen-fixing legumes in the associated vegetation (putative host species).A
max forB. trixago ranged from 7.7 to 18.8 mol m-2 s-1; similar rates were measured for a second hemiparasiteParentucellia viscosa, and both species were within the range of rates measured for six putative hosts (10.6–19.2 mol m-2 s-1). Fertilization of unattachedB. trixago plants with inorganic nitrogen (ammonium nitrate) elicited neither the growth nor the photosynthetic responses observed in plants considered to be parasitic on legumes and in receipt of an enriched organic nitrogen supply. Both hemiparasites had high diurnal leaf conductances (g
s) (469–2291 mmol m-2 s-1) and were at the upper end of the range of those measured in putative hosts (409–879 mmol m-2 s-1). In contrast with the latter, high nocturnal rates ofg
s were also recorded for the two hemiparasites (517–1862 mmol m-2 s-1). There was no clear relationship between eitherA
max orN
1 and eitherg
s, transpiration (E) or water use efficiency (A
max/E) inB. trixago plants. The economics of water loss appear to be independent of both the supply of nitrogen from the host and autotrophic carbon fixation. 相似文献
109.
Characterization of human immunodeficiency virus type 1 integrase expressed in Escherichia coli and analysis of variants with amino-terminal mutations. 总被引:43,自引:30,他引:13 下载免费PDF全文
Replication of a retroviral genome depends upon integration of the viral DNA into a chromosome of the host cell. The integration reaction is mediated by integrase, a viral enzyme. Human immunodeficiency virus type 1 integrase was expressed in Escherichia coli and purified to near homogeneity. Optimum conditions for the integration and 3'-end-processing activities of integrase were characterized by using an in vitro assay with short, double-stranded oligonucleotide substrates. Mutants containing amino acid substitutions within the HHCC region, defined by phylogenetically conserved pairs of histidine and cysteine residues near the N terminus, were constructed and characterized by using three assays: 3'-end processing, integration, and the reverse of the integration reaction (or disintegration). Mutations in the conserved histidine and cysteine residues abolished both integration and processing activities. Weak activity in both assays was retained by two other mutants containing substitutions for less highly conserved amino acids in this region. All mutants retained activity in the disintegration assay, implying that the active site for DNA cleavage-ligation is not located in this domain and that the HHCC region is not the sole DNA-binding domain in the protein. However, the preferential impairment of processing and integration rather than disintegration by mutations in the HHCC region is consistent with a role for this domain in recognizing features of the viral DNA. This hypothesis is supported by the results of disintegration assays performed with altered substrates. The results support a model involving separate viral and target DNA-binding sites on integrase. 相似文献
110.
Louis-Marie Vincent 《Acta biotheoretica》1993,41(1-2):139-145
A new approach to information is proposed with the intention of providing a conceptual tool adapted to biology, including a semantic value.Information involves a material support as well as a significance, adapted to the cognitive domain of the receiver and/or the transmitter. A message does not carry any information, only data. The receiver makes an identification by a procedure of recognition of the forms, which activate previously learned significance. This treatment leads to a new significance (or new knowledge).The notion of a probabilistic event is abandoned. The quantity of information is the product of the quantity of data (probability of recognition of the message) times the value of the significance, determined by its semantic level. 相似文献