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51.
52.
Flash photolysis of DM-nitrophen generates an extremely large [Ca2+] transient ("Ca2+ spike") at the start of each Ca2+ "step." The Ca2+ spike greatly increases the speed of activation of the ryanodine receptor channel ("supercharging") and could be responsible for apparent channel adaptation. 相似文献
53.
The serum response factor nuclear localization signal: general implications for cyclic AMP-dependent protein kinase activity in control of nuclear translocation. 总被引:5,自引:1,他引:4
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C Gauthier-Rouvire M Vandromme N Lautredou Q Q Cai F Girard A Fernandez N Lamb 《Molecular and cellular biology》1995,15(1):433-444
We have identified a basic sequence in the N-terminal region of the 67-kDa serum response factor (p67SRF or SRF) responsible for its nuclear localization. A peptide containing this nuclear localization signal (NLS) translocates rabbit immunoglobulin G (IgG) into the nucleus as efficiently as a peptide encoding the simian virus 40 NLS. This effect is abolished by substituting any two of the four basic residues in this NLS. Overexpression of a modified form of SRF in which these basic residues have been mutated confirms the absolute requirement for this sequence, and not the other basic amino acid sequences adjacent to it, in the nuclear localization of SRF. Since this NLS is in close proximity to potential phosphorylation sites for the cAMP-dependent protein kinase (A-kinase), we further investigated if A-kinase plays a role in the nuclear location of SRF. The nuclear transport of SRF proteins requires basal A-kinase activity, since inhibition of A-kinase by using either the specific inhibitory peptide PKIm or type II regulatory subunits (RII) completely prevents the nuclear localization of plasmid-expressed tagged SRF or an SRF-NLS-IgG conjugate. Direct phosphorylation of SRF by A-kinase can be discounted in this effect, since mutation of the putative phosphorylation sites in either the NLS peptide or the encoded full-length SRF protein had no effect on nuclear transport of the mutants. Finally, in support of an implication of A-kinase-dependent phosphorylation in a more general mechanism affecting nuclear import, we show that the nuclear transport of a simian virus 40-NLS-conjugated IgG or purified cyclin A protein is also blocked by inhibition of A-kinase, even though neither contains any potential sites for phosphorylation by A-kinase or can be phosphorylated by A-kinase in vitro. 相似文献
54.
Alterations in Phosphatidylcholine Metabolism of Stretch-Injured Cultured Rat Astrocytes 总被引:1,自引:1,他引:0
Robert G. Lamb Courtney C. Harper Jerry S. McKinney Beverly A. Rzigalinski Earl F. Ellis 《Journal of neurochemistry》1997,68(5):1904-1910
Abstract: The primary objective of this study was to determine the influence of stretch-induced cell injury on the metabolism of cellular phosphatidylcholine (PC). Neonatal rat astrocytes were grown to confluency in Silastic-bottomed tissue culture wells in medium that was usually supplemented with 10 µM unlabeled arachidonate. Cell injury was produced by stretching (5–10 mm) the Silastic membrane with a 50-ms pulse of compressed air. Stretch-induced cell injury increased the incorporation of [3H]choline into PC in an incubation time- and stretch magnitude-dependent manner. PC biosynthesis was increased three- to fourfold between 1.5 and 4.5 h after injury and returned to control levels by 24 h postinjury. Stretch-induced cell injury also increased the activity of several enzymes involved in the hydrolysis [phospholipase A2 (EC 3.1.1.4) and C (PLC; EC 3.1.4.3)] and biosynthesis [phosphocholine cytidylyltransferase (PCT; EC 2.7.7.15)] of PC. Stretch-induced increases in PC biosynthesis and PCT activity correlated well (r = 0.983) and were significantly reduced by pretrating (1 h) the cells with an iron chelator (deferoxamine) or scavengers of reactive oxygen species such as superoxide dismutase and catalase. The stretch-dependent increase in PC biosynthesis was also reduced by antioxidants (vitamin E, vitamin E succinate, vitamin E phosphate, melatonin, and n-acetylcysteine). Arachidonate-enriched cells were more susceptible to stretch-induced injury because lactate dehydrogenase release and PC biosynthesis were significantly less in non-arachidonate-enriched cells. In summary, the data suggest that stretch-induced cell injury is (a) a result of an increase in the cellular level of hydroxyl radicals produced by an iron-catalyzed Haber-Weiss reaction, (b) due in part to the interaction of oxyradicals with the polyunsaturated fatty acids of cellular phospholipids such as PC, and (c) reversible as long as the cell's membrane repair functions (PC hydrolysis and biosynthesis) are sufficient to repair injured membranes. These results suggest that stretch-induced cell injury in vitro may mimic in part experimental traumatic brain injury in vivo because alterations in cellular PC biosynthesis and PLC activity are similar in both models. Therefore, this in vitro model of stretch-induced injury may supplement or be a reasonable alternative to some in vivo models of brain injury for determining the mechanisms by which traumatic cell injury results in cell dysfunction. 相似文献
55.
A highly conserved nuclear gene for low-level phylogenetics: elongation factor-1 alpha recovers morphology-based tree for heliothine moths 总被引:8,自引:2,他引:6
Cho S; Mitchell A; Regier JC; Mitter C; Poole RW; Friedlander TP; Zhao S 《Molecular biology and evolution》1995,12(4):650-656
Molecular systematists need increased access to nuclear genes. Highly
conserved, low copy number protein-encoding nuclear genes have attractive
features for phylogenetic inference but have heretofore been applied mostly
to very ancient divergences. By virtue of their synonymous substitutions,
such genes should contain a wealth of information about lower-level
taxonomic relationships as well, with the advantage that amino acid
conservatism makes both alignment and primer definition straightforward. We
tested this postulate for the elongation factor-1 alpha (EF-1 alpha) gene
in the noctuid moth subfamily Heliothinae, which has probably diversified
since the middle Tertiary. We sequenced 1,240 bp in 18 taxa representing
heliothine groupings strongly supported by previous morphological and
allozyme studies. The single most parsimonious gene tree and the
neighbor-joining tree for all nucleotides show almost complete concordance
with the morphological tree. Homoplasy and pairwise divergence levels are
low, transition/transversion ratios are high, and phylogenetic information
is spread evenly across gene regions. The EF-1 alpha gene and presumably
other highly conserved genes hold much promise for phylogenetics of
Tertiary age eukaryote groups.
相似文献
56.
Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation. 相似文献
57.
Summary Tests made to utilize lignocellulosics as a substrate for the production of cellulases showed that the enzyme production from steam and explosion decompressed aspen wood (SED) by Tricoderma reesei RUT-C30 was low, and the enzyme system produced was deficient in exoglucanase and -glucosidase activities. Mixing this substrate with 10–20% pure cellulose lessened this deficiency and improved enzyme production. The enzyme system produced from the mixed substrate was rich in xylanase and had saccharifying ability equal to that produced in medium containing pure cellulose. 相似文献
58.
A structural comparison of the A and B subunits of Griffonia simplicifolia I isolectins 总被引:1,自引:0,他引:1
A structural comparison between the A and B subunits of the five tetrameric Griffonia simplicifolia I isolectins (A4, A3B, A2B2, AB3, B4) was undertaken to determine the extent of homology between the subunits. The first 25 N-terminal amino acids of both A and B subunits were determined following the enzymatic removal of N-terminal pyroglutamate blocking groups with pyroglutamate aminopeptidase. Although 21 amino acids were common to both subunits, there were four unique amino acids in the N-terminal sequence of A and B. Residues 8, 9, 17, and 19 were asparagine, leucine, lysine, and asparagine in subunit A and threonine, phenylalanine, glutamic acid, and serine in subunit B. The last six C-terminal amino acids, released by digestion with carboxypeptidase Y, were the same for both subunits: Arg-(Phe, Val)-Leu-Thr-Ser-COOH. Subunit B, which contains one methionyl residue, was cleaved by cyanogen bromide into two fragments, a large (Mr = 31,000) and a small (Mr = 2700) polypeptide. Failure of the small fragment to undergo manual Edman degradation indicated an N-terminal blocking group, presumably pyroglutamate. Both subunits were digested with trypsin and the tryptic peptides were analyzed using reverse-phase HPLC. Tryptic glycopeptides were identified by labeling the carbohydrate moiety of the A and B subunit using sodium [3H] borohydride. Cysteine-containing tryptic peptides were similarly identified by using [1-14C]iodoacetamide. Approximately 30% of the tryptic peptides were common to both subunits. Thus, although the N- and C-terminal regions of A and B are similar, the subunits each possess unique sequences. 相似文献
59.
60.