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961.
Previously we have reported that induction of apoptosis in Jurkat cells results in an inhibition of overall protein synthesis with the selective and rapid cleavage of eukaryotic initiation factor (eIF) 4GI. For the cleavage of eIF4GI, caspase-3 activity is both necessary and sufficient in vivo, in a process which does not require signaling through the p38 MAP kinase pathway. We now show that activation of the Fas/CD95 receptor promotes an early, transient increase in the level of eIF2alpha phosphorylation, which is temporally correlated with the onset of the inhibition of translation. This is associated with a modest increase in the autophosphorylation of the protein kinase activated by double-stranded RNA. Using a Jurkat cell line that is deficient in caspase-8 and resistant to anti-Fas-induced apoptosis, we show that whilst the cleavage of eIF4GI is caspase-8-dependent, the enhancement of eIF2alpha phosphorylation does not require caspase-8 activity and occurs prior to the cleavage of eIF4GI. In addition, activation of the Fas/CD95 receptor results in the caspase-8-dependent dephosphorylation and degradation of p70(S6K), the enhanced binding of 4E-BP1 to eIF4E, and, at later times, the cleavage of eIF2alpha. These data suggest that apoptosis impinges upon the activity of several polypeptides which are central to the regulation of protein synthesis and that multiple signaling pathways are involved in vivo. 相似文献
962.
An arabinogalactan-protein (AGP) was purified from differentiating xylem of loblolly pine (Pinus taeda L.) and the N-terminal sequence used to identify a cDNA clone. The protein, PtaAGP3, was not coded for by any previously identified AGP-like genes. Moreover, PtaAGP3 was abundantly and preferentially expressed in differentiating xylem. The encoded protein contains four domains, a signal
peptide, a cleaved hydrophilic region, a region rich in serine, alanine, and proline/hydroxyproline, and a hydrophobic C-terminus.
It is postulated to contain a GPI (glycosylphosphatidylinositol) anchor site. If the protein is cleaved at the putative GPI
anchor site, as has been observed in other classical AGPs, all but the Ser-Ala-Pro/Hyp-rich domain may be missing from the
mature protein. Xylem-specific AGPs are hypothesized to be involved in xylem development.
Received: 29 July 1999 / Accepted: 19 August 1999 相似文献
963.
Increase in Endogenous and Exogenous Cyclic AMP Levels Inhibits Sclerotial Development in Sclerotinia sclerotiorum 总被引:3,自引:0,他引:3
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Growth and development of a wild-type Sclerotinia sclerotiorum isolate were examined in the presence of various pharmacological compounds to investigate signal transduction pathways that influence the development of sclerotia. Compounds known to increase endogenous cyclic AMP (cAMP) levels in other organisms by inhibiting phosphodiesterase activity (caffeine and 3-isobutyl-1-methyl xanthine) or by activating adenylate cyclase (NaF) reduced or eliminated sclerotial development in S. sclerotiorum. Growth in the presence of 5 mM caffeine correlated with increased levels of endogenous cAMP in mycelia. In addition, incorporation of cAMP into the growth medium decreased or eliminated the production of sclerotia in a concentration-dependent manner and increased the accumulation of oxalic acid. Inhibition of sclerotial development was cAMP specific, as exogenous cyclic GMP, AMP, and ATP did not influence sclerotial development. Transfer of developing cultures to cAMP-containing medium at successive time points demonstrated that cAMP inhibits development prior to or during sclerotial initiation. Together, these results indicate that cAMP plays a role in the early transition between mycelial growth and sclerotial development. 相似文献
964.
Structural Organization of Virulence-Associated Plasmids of Yersinia pestis 总被引:6,自引:0,他引:6
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Ping Hu Jeffrey Elliott Paula McCready Evan Skowronski Jeffrey Garnes Arthur Kobayashi Robert R. Brubaker Emilio Garcia 《Journal of bacteriology》1998,180(19):5192-5202
The complete nucleotide sequence and gene organization of the three virulence plasmids from Yersinia pestis KIM5 were determined. Plasmid pPCP1 (9,610 bp) has a GC content of 45.3% and encodes two previously known virulence factors, an associated protein, and a single copy of IS100. Plasmid pCD1 (70,504 bp) has a GC content of 44.8%. It is known to encode a number of essential virulence determinants, regulatory functions, and a multiprotein secretory system comprising the low-calcium response stimulation that is shared with the other two Yersinia species pathogenic for humans (Y. pseudotuberculosis and Y. enterocolitica). A new pseudogene, which occurs as an intact gene in the Y. enterocolitica and Y. pseudotuberculosis-derived analogues, was found in pCD1. It corresponds to that encoding the lipoprotein YlpA. Several intact and partial insertion sequences and/or transposons were also found in pCD1, as well as six putative structural genes with high homology to proteins of unknown function in other yersiniae. The sequences of the genes involved in the replication of pCD1 are highly homologous to those of the cognate plasmids in Y. pseudotuberculosis and Y. enterocolitica, but their localization within the plasmid differs markedly from those of the latter. Plasmid pMT1 (100,984 bp) has a GC content of 50.2%. It possesses two copies of IS100, which are located 25 kb apart and in opposite orientations. Adjacent to one of these IS100 inserts is a partial copy of IS285. A single copy of an IS200-like element (recently named IS1541) was also located in pMT1. In addition to 5 previously described genes, such as murine toxin, capsule antigen, capsule anchoring protein, etc., 30 homologues to genes of several bacterial species were found in this plasmid, and another 44 open reading frames without homology to any known or hypothetical protein in the databases were predicted. 相似文献
965.
966.
Yasuji Sawada Yoshiki Maeda Ikuo Takeuchi Jeffrey Williams Yasuo Maeda 《Development, growth & differentiation》1998,40(1):113-120
The following was recently reported by Bonner et al. (1995): (1) Rapid differentiation occurred into two zones in Dictyostelium discoideum cells confined in a fine glass capillary. The cells in the anterior zone exposed to the air appear similar to prestalk cells, while the posterior zone isolated from the air mimics prespore cells. (2) The volumes of the two zones are proportional to each other for different sized cell masses, and the proportion is the same as that in normal migrating slugs. We investigated the nature of this newly discovered rapid differentiation in a slightly modified geometry. Exponentially growing cells were harvested, washed to remove external nutrients, and pelleted by centrifugation. Subsequently, a small drop of the pelleted (starved) cells was placed on a slide glass and then confined in a two-dimensional space between the slide glass and a coverslip, with help of spacers whose thickness varied from 25 to 100 μm. As a result, a dark zone, which looked optically different, emerged within several minutes in the periphery of the disc of the confined cells, corresponding to the zonation in a capillary as previously reported. When the width of the peripheral zone was measured for more than 30 samples of different diameters for each thickness of the spacers, the width was found to be always about 100 μm, irrespective of the size difference of the cell mass placed. This seems to be contradictory to the previous observation made by Bonner et al. (1995). We also examined oxygen concentration dependence on the zone width. The zone width was found to be independent of the oxygen concentration at low concentrations, but increased rapidly at high concentrations. A reaction-diffusion mechanism for formation of the zone and possible involvement of atmospheric oxygen (O2 ) in the initial steps of cell differentiation and pattern formation is discussed. 相似文献
967.
Maryse Bailly Lin Yan George M. Whitesides John S. Condeelis Jeffrey E. Segall 《Experimental cell research》1998,241(2):285
We report here the first direct observation of chemotaxis to EGF by rat mammary carcinoma cells. When exposed to a gradient of EGF diffusing from a micropipette, MTLn3 cells displayed typical ameboid chemotaxis, extending a lamellipod-like protrusion and moving toward the pipette. Using a homogeneous upshift in EGF to model stimulated lamellipod extension (J. E. Segallet al.,1996,Clin. Exp. Metastasis14, 61–72), we analyzed the relationship between adhesion and chemoattractant-stimulated protrusion. Exposure to EGF led to a rapid remodeling of the adhesive contacts on adherent cells, in synchrony with extension of a flat lamellipod over the substratum. EGF-stimulated lamellipods still extended in the presence of adhesion-blocking peptides or over nonadhesive surfaces. They were, however, slightly shorter and retracted rapidly under those conditions. The major protrusive structure observed on well-spread, adherent cells, after EGF stimulation was a flat broad lamellipod, whether or not in contact with the substratum, while cells in suspension showed transient protrusive activity over the entire cell surface. We conclude that the initial adhesive status of the cell conditions the shape of the outcoming protrusion. Altogether our results suggest that, although adhesive contacts are not necessary for lamellipod extension, they play a role in stabilizing the protrusion as well as in the control of its final shape and amplitude. 相似文献
968.
Plants and protozoa contain a unique family of calcium-dependent protein kinases (CDPKs) which are defined by the presence of a carboxyl-terminal calmodulin-like regulatory domain. We present biochemical evidence indicating that at least one member of this kinase family can be stimulated by 14-3-3 proteins. Isoform CPK-1 from the model plant Arabidopsis thaliana was expressed as a fusion protein in E. coli and purified. The calcium-dependent activity of this recombinant CPK-1 was shown to be stimulated almost twofold by three different 14-3-3 isoforms with 50% activation around 200 nM. 14-3-3 proteins bound to the purified CPK-1, as shown by binding assays in which either the 14-3-3 or CPK-1 were immobilized on a matrix. Both the 14-3-3 binding and activation of CPK-1 were specifically disrupted by a known 14-3-3 binding peptide LSQRQRSTpSTPNVHMV (IC50=30 μM). These results raise the question of whether 14-3-3 can modulate the activity of CDPK signal transduction pathways in plants. 相似文献
969.
970.
Drosophila Centrosomin Protein is Required for Male Meiosis and Assembly of the Flagellar Axoneme 总被引:1,自引:0,他引:1
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Kaijun Li Eugene Yujun Xu Jeffrey K. Cecil F. Rudolf Turner Timothy L. Megraw Thomas C. Kaufman 《The Journal of cell biology》1998,141(2):455-467
Centrosomes and microtubules play crucial roles during cell division and differentiation. Spermatogenesis is a useful system for studying centrosomal function since it involves both mitosis and meiosis, and also transformation of the centriole into the sperm basal body. Centrosomin is a protein localized to the mitotic centrosomes in Drosophila melanogaster. We have found a novel isoform of centrosomin expressed during spermatogenesis. Additionally, an anticentrosomin antibody labels both the mitotic and meiotic centrosomes as well as the basal body. Mutational analysis shows that centrosomin is required for spindle organization during meiosis and for organization of the sperm axoneme. These results suggest that centrosomin is a necessary component of the meiotic centrosomes and the spermatid basal body. 相似文献