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81.
Translatable RNA Populations Associated with Maintenance of Primary Root Elongation and Inhibition of Mesocotyl Elongation by Abscisic Acid in Maize Seedlings at Low Water Potentials 总被引:4,自引:2,他引:2 下载免费PDF全文
Previous work indicated that accumulation of abscisic acid (ABA) acts differentially to maintain elongation of the primary root and inhibit elongation of the mesocotyl of maize (Zea mays L.) seedlings at low water potentials ([psi]w). Subsequent results indicated specific locations in the elongation zones where elongation is maintained, inhibited, or unaffected by endogenous ABA at low [psi]w. This information was utilized in this study to identify in vitro translation products of RNA associated with the maintenance or inhibition of elongation in the primary root and mesocotyl, respectively, by endogenous ABA at low [psi]w. The results distinguished products associated specifically with the elongation responses from those nonspecifically associated with ABA accumulation or low [psi]w, as well as normal cell development and maturation. In the primary root, the maintenance of elongation at low [psi]w by ABA was associated with the maintenance of expression of three products that were also expressed during elongation at high [psi]w, the expression of a novel product, and the suppression of two products. In the mesocotyl, the inhibition of elongation by ABA after transplanting to low [psi]w was associated with the induction of a novel translation product. However, the induction of this product, as well as accumulation of ABA and inhibition of elongation, occurred without a decline in tissue water content. The results demonstrate the necessity of examining the association of gene expression with elongation responses to low [psi]w with a high degree of spatial resolution. 相似文献
82.
Effect of different donor cells on human immunodeficiency virus type 1 replication and selection in vitro. 总被引:8,自引:7,他引:1 下载免费PDF全文
We sought to determine the effects of different host cells on human immunodeficiency virus type 1 (HIV-1) infection in vitro. First, 17 primary viruses of various phenotypes were examined for replicative capacity in peripheral blood mononuclear cells (PBMC) from 10 healthy donors. While the range of infection was variable over a 40-fold range, it was substantially less than that previously reported (L. M. Williams and M. W. Cloyd, Virology 184:723-728, 1991). In particular, no donor cells demonstrated total resistance to HIV-1 infection. We next cocultured PBMC from an HIV-1-infected patient with stimulated PBMC from three healthy donors to determine the effect of host cells on selection for a particular HIV-1 quasispecies. By using DNA sequencing, it was found that the dominant quasispecies (AD30-15) after culture was nearly identical in the cells of different donors. Furthermore, after 6 months in vivo, the patient developed a dominant proviral population in PBMC that was most closely related to the quasispecies preferentially selected in vitro, although this quasispecies was only a minor fraction of the sequences present earlier in PBMC. In subsequent biological characterizations, it was found that AD30-15 grew much better in PBMC and macrophages than did other related quasispecies. Hence, we conclude that the primary mechanism of in vitro selection for a particular HIV-1 variant in this case is mediated by the phenotypic properties of the virus and is less dependent on host cell origin. The findings reported here have important practical implications for studies of HIV-1 replication in primary cells derived from healthy donors. 相似文献
83.
A human monoclonal antibody to a complex epitope in the V3 region of gp120 of human immunodeficiency virus type 1 has broad reactivity within and outside clade B. 总被引:21,自引:18,他引:3 下载免费PDF全文
J P Moore A Trkola B Korber L J Boots J A Kessler nd F E McCutchan J Mascola D D Ho J Robinson A J Conley 《Journal of virology》1995,69(1):122-130
We have used virus neutralization and antibody-binding techniques to define the epitope for a human monoclonal antibody, designated 19b, within the V3 region of the gp120 surface glycoprotein of human immunodeficiency virus type 1. Unusually, the 19b epitope encompasses residues on both flanks of the V3 loop. However, 19b binding to gp120 is independent of sequences at the crown of the V3 loop, provided that they are compatible with the formation of a type II beta turn that is presumably necessary to juxtapose the antigenic residues on the V3 flanks. By comparing the V3 sequences of virus gp120s able and unable to bind 19b, we were able to define the canonical 19b epitope as -I----G--FY-T, where residues at the positions indicated by the gaps do not contribute directly to the 19b-binding site. A few conservative substitutions at the more critical residues are also compatible with 19b binding. Inspection of V3 sequences in the human immunodeficiency virus database indicated that the canonical 19b epitope is well conserved among isolates from the North American-European clade B and also among clade E isolates from Thailand and clade F isolates from Brazil. A minority of gp120s from clades A and C also possess the 19b epitope. Consistent with the theoretical predictions of its cross-clade reactivity, 19b was found to bind to gp120s from clades A, B, C, E, and F in immunoassays. However, 19b was not able to reduce the infectivity of primary viruses from clades A, E, and F that were predicted to possess the 19b epitope and only modestly reduced the infectivity of a clade C virus at low input virus concentrations. Cross-clade neutralization via V3-directed antibodies may, therefore, be difficult, even if the antibodies show broad reactivities in binding assays and the viruses theoretically possess the relevant binding site. 相似文献
84.
Staphylococcus haemolyticus contains two D-glutamic acid biosynthetic activities, a glutamate racemase and a D-amino acid transaminase. 下载免费PDF全文
Two D-glutamic acid biosynthetic activities, glutamate racemase and D-amino acid transaminase, have been described previously for bacteria. To date, no bacterial species has been reported to possess both activities. Genetic complementation studies using Escherichia coli WM335, a D-glutamic acid auxotroph, and cloned chromosomal DNA fragments from Staphylococcus haemolyticus revealed two distinct DNA fragments containing open reading frames which, when present, allowed growth on medium without exogenous D-glutamic acid. Amino acid sequences of the two open reading frames derived from the DNA nucleotide sequences indicated extensive identity with the amino acid sequence of Pediococcus pentosaceous glutamate racemase in one case and with that of the D-amino acid transaminase of Bacillus spp. in the second case. Enzymatic assays of lysates of E. coli WM335 strains containing either the cloned staphylococcal racemase or transminase verified the identities of these activities. Subsequent DNA hybridization experiments indicated that Staphylococcus aureus, in addition to S. haemolyticus, contained homologous chromosomal DNA for each of these genes. These data suggest that S. haemolyticus, and probably S. aureus, contains genes for two D-glutamic acid biosynthetic activities, a glutamate racemase (dga gene) and a D-amino acid transaminase (dat gene). 相似文献
85.
86.
Abstract: The α subunit of Gz (αz) harbors two N-terminal serine residues (at positions 16 and 27) that serve as protein kinase C-mediated phosphorylation sites. The cognate residues in the α subunit of Gt1 provide binding surfaces for the β1 subunit. We used three serine-to-alanine mutants of αz to investigate the functional importance of the two N-terminal serine residues. Wild-type or mutant αz was transiently coexpressed with different receptors and adenylyl cyclase isozymes in human embryonic kidney 293 cells, and agonist-dependent regulation of cyclic AMP accumulation was examined in a setting where all endogenous α subunits of Gi were inactivated by pertussis toxin. Replacement of one or both serine residues by alanine did not alter the ability of αz to interact with δ-opioid, dopamine D2, or adenosine A1 receptors. Its capacity to inhibit endogenous and type VI adenylyl cyclases was also unaffected. Functional release of βγ subunits from the mutant αz subunits was not impaired because they transduced βγ-mediated stimulation of type II adenylyl cyclase. Constitutively active mutants of all four αz subunits were constructed by the introduction of a Q205L mutation. The activated mutants showed differential abilities to inhibit human choriogonadotropin-mediated cyclic AMP accumulation in luteinizing hormone receptor-transfected cells. Loss of both serine residues, but not either one alone, impaired the receptor-independent inhibition of adenylyl cyclase by the GTPase-deficient mutant. Thus, replacement of the amino-terminal serine residues of αz has no apparent effect on receptor-mediated responses, but these serine residues may be essential for ensuring transition of αz into the active conformation. 相似文献
87.
88.
89.
The histidine-binding protein J of Salmonella typhimurium binds L-histidine as a first step in the high-affinity active transport of this amino acid across the cytoplasmic membrane. High-resolution nuclear magnetic resonance spectroscopy has been used to monitor the conformation of histidine-binding protein J in the presence and absence of substrate. Evidence is presented to show that this binding protein undergoes a conformational change involving a substantial number of amino-acid residues (including tryptophans) in the presence of L-histidine and that this change is specific for L-histidine. In order to monitor the involvement of tryptophan residues in the substrate-induced conformational change, 5-fluorotryptophan has been incorporated biosynthetically into the histidine-binding protein J using a tryptophan autotroph of Salmonella typhimurium. There are no significant differences in the conformation and binding activity between the 5-fluorotryptophan-labeled and the normal histidine-binding protein J. Proton and fluorine-19 nuclear magnetic resonance studies of the 5-fluorotryptophan-labeled binding protein show that at least one (and possibly two) of the tryptophan residues undergo(es) a change toward a more hydrophobic environment in the presence of L-histidine. These observations are supported by fluorescence data and by differences in the reactivity of the tryptophan residues of this protein toward N-bromosuccinimide in the presence and absence of substrate. The present results are consistent with models for the action of periplasmic-binding proteins in shock-sensitive transport systems of gram-negative bacteria which require a substrate-induced conformational change prior to the energy-dependent translocation of substrates. 相似文献
90.
Dynamic light scattering has been used to study the temperature dependence of Ca2+-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca2+ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca2+ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca2+ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca2+ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca2+, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca2+ concentration, and identical to that with pure phosphatidylserine in excess Ca2+. The results imply that Ca2+-induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains. 相似文献