Differential Expression of the Two Subunits of Tomato Polygalacturonase Isoenzyme 1 in Wild-Type and rin Tomato Fruit

The [beta] subunit of tomato (Lycopersicon esculentum Mill.) fruit polygalacturonase 1 is a cell wall glycoprotein that binds to and apparently regulates the catalytic PG2 polypeptide in vivo. [beta] Subunit and polygalacturonase 2 (PG2) expression have been investigated in both wild-type and ripening inhibitor (rin) mutant fruit. During fruit development and ripening, [beta] subunit expression was unrelated to expression of the catalytic PG2 protein. In wild-type fruit, [beta] subunit mRNA and protein were first detected early in development and increased to maximal levels before PG2 mRNA and protein were detected. At the onset of ripening [beta] subunit mRNA decreased dramatically, but [beta] subunit protein levels remained stable. In rin fruit, which fail to ripen, [beta] subunit expression was similar to that in wild type, although PG2 mRNA and protein were not detected. These data suggest that [beta] subunit expression is ethylene independent and regulated primarily by developmental cues. This conclusion is supported by results from ethylene-treated immature (20 days after pollination) wild-type and rin fruit in which no significant differences were observed in [beta] subunit expression patterns in response to ethylene treatment. Surprisingly, RNA blot analysis indicated that catalytic PG2 mRNA was induced in immature rin fruit after 3 d of exogenous ethylene treatment. In addition, [beta] subunit mRNA and protein were also detected at lower levels in root, leaf, and flower tissues of both genotypes, suggesting a broader functional role for the protein.

Catalytic formation of a nitrogenase iron-sulfur cluster

Biological nitrogen fixation is catalyzed by nitrogenase, an enzyme comprised of two component proteins called the Fe protein and the MoFe protein. Both nitrogenase component proteins contain metalloclusters. The Azotobacter vinelandii nifS gene product (NifS), which is required for full activation of the nitrogenase component proteins, is a pyridoxal phosphate enzyme and is able to catalyze the desulfurization of L-cysteine to yield sulfur and L-alanine (Zheng, L., White, R. H., Cash, V.L., Jack, R.F., and Dean, D.R. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2754-2758). An enzyme-bound persulfide that was identified as an intermediate in the cysteine desulfurization reaction catalyzed by NifS has been suggested as a possible S-donor in formation of the iron-sulfide cores of the nitrogenase metalloclusters. In the present work it is shown that NifS is able to effectively catalyze activation of an apo-form of the Fe protein that was prepared by removal of its Fe4S4 cluster using the chelator, alpha,alpha'-dipyridyl. The reconstitution reaction includes apo-Fe protein, NifS, L-cysteine, ferrous ion, dithiothreitol, and MgATP. Reconstitution of the inactive apo-Fe protein catalyzed by NifS results in 80-95% recovery of the original activity and yields an Fe protein having the normal electron paramagnetic resonance spectra properties associated with the Fe protein's Fe4S4 cluster. An altered NifS protein, NifS-Ala325, which lacks the desulfurase activity and is unable to from the NifS-bound persulfide, is not able to catalyze reactivation of the apo-Fe protein. These in vitro results support the proposal that NifS activity provides the inorganic sulfide necessary for in vivo formation of the nitrogenase metalloclusters. Moreover, because NifS has recently been shown to be a member of a highly homologous gene family, it appears that pyridoxal phosphate chemistry might play a general role in iron-sulfur cluster assembly.

Mechanism for the desulfurization of L-cysteine catalyzed by the nifS gene product

The nifS gene product (NIFS) is a pyridoxal phosphate binding enzyme that catalyzes the desulfurization of L-cysteine to yield L-alanine and sulfur. In Azotobacter vinelandii this activity is required for the full activation of the nitrogenase component proteins. Because the nitrogenase component proteins, Fe protein and MoFe protein, both contain metalloclusters which are required for their respective activities, it is suggested that NIFS participates in the biosynthesis of the nitrogenase metalloclusters by providing the inorganic sulfur required for Fe-S core formation [Zheng, L., White, R. H., Cash, V. L. Jack, R. F., & Dean, D. R. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2754-2758]. In the present study the mechanism for the desulfurization of L-cysteine catalyzed by NIFS was determined in the following ways. First, the substrate analogs, L-allylglycine and vinylglycine, were shown to irreversibly inactivate NIFS by formation of a gamma-methylcystathionyl or cystathionyl residue, respectively, through nucleophilic attack by an active site cysteinyl residue on the corresponding analog-pyridoxal phosphate adduct. Second, this reactive cysteinyl residue, which is required for L-cysteine desulfurization activity, was identified as Cys325 by the specific alkylation of that residue and by site-directed mutagenesis experiments. Third, the formation of an enzyme-bound cysteinyl persulfide was identified as an intermediate in the NIFS-catalyzed reaction. Fourth, evidence was obtained for an enamine intermediate in the formation of L-alanine.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequential activation of phospholipase-C and -D in agonist-stimulated gonadotrophs

The contributions of phospholipase-C and -D to diacylglycerol (DG) formation during agonist-induced cell signaling were investigated in rat pituitary cells and alpha T3-1 gonadotrophs. In both cell types, GnRH caused a biphasic increase in DG formation, with an initial spike within 60 sec, followed by a larger and sustained rise to reach a second peak after 15 min of stimulation. Both phases of DG production were temporally correlated with inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] formation, consistent with the dependence of DG formation on phospholipase-C-mediated phosphoinositide hydrolysis. However, the ability of GnRH to stimulate phosphatidylethanol (PEt) in the presence of ethanol suggested that phospholipase-D may also participate in DG formation. Two inhibitors of phospholipase-C-dependent phosphoinositide hydrolysis, U73122 and neomycin sulfate, reduced the PEt as well as the Ins(1,4,5)P3 response to GnRH, indicating that phospholipase-D is activated during phospholipase-C-dependent signaling in pituitary gonadotrophs. The production of both DG and PEt was increased by treatment with the active phorbol ester phorbol 12-myristate 13-acetate (PMA), but not with inactive 4 alpha-phorbol 13-didecanoate, indicating that stimulation of protein kinase-C leads to activation of phospholipase-D. In accord with this, GnRH- and PMA-induced elevations of DG and PEt production were attenuated or abolished in protein kinase-C-depleted cells. In contrast, short and long term stimulation with PMA had no effect on basal inositol phosphate production. Also, GnRH-induced inositol phosphate production was not affected by protein kinase-C depletion. Finally, U73122 and neomycin sulfate did not inhibit PMA-induced PEt formation. These data indicate that GnRH activates a dual phospholipase pathway in a sequential and synchronized manner; phospholipase-C initiates the biphasic increase in Ins(1,4,5)P3 and DG formation, and protein kinase-C mediates the integration of phospholipase-D into the signaling response during the sustained phase of agonist stimulation.

Optimization by trees on simple adaptive landscapes

We evaluate the optimizing ability (rate of adaptation) of trees on simple adaptive landscapes. At points away from a peak, there is a strong negative relationship between rate of adaptation and tree precision P, a relationship that is independent of the size of the tree. P measures the variability among trial solutions generated by the tree: high precision trees have low variability, low precision trees have high variability. Near a peak, the situation reverses, with high precision trees showing higher rates of adaptation than low precision trees; however, for all trees, the absolute rate of adaptation is uniformly low. On multiple-peak landscapes, the probability of crossing an adaptive valley from a lower peak to a higher peak is also negatively correlated with tree precision. These results suggest that under a wide range of conditions, trees with low precision are, on average, the best optimizers.

Stimulation of the intracellular killing of Staphylococcus aureus by human monocytes mediated by Fc gamma receptors I and II

Previous studies have shown that intracellular killing of bacteria by monocytes is stimulated by interaction between IgG and Fc gamma receptors (Fc gamma R) in the membrane of these cells. In the present study anti-Fc gamma R monoclonal antibodies (mAb) were used to investigate the relative contributions of the various classes of Fc gamma R to the intracellular killing of Staphylococcus aureus by human monocytes and the biochemical pathways involved. Anti-Fc gamma RI or anti-Fc gamma RII mAb, but not anti-Fc gamma RIII mAb, efficiently stimulated the intracellular killing of bacteria by monocytes. Cross-linking Fc gamma RI or Fc gamma RII, but not Fc gamma RIII, on monocytes with mouse anti-Fc gamma R mAb followed by bridging with F(ab')2 fragments of goat anti-mouse IgG enhanced this process. Since the NADPH oxidase inhibitor diphenyleneiodonium blocked the Fc gamma R-mediated intracellular killing of S. aureus, oxygen-dependent bactericidal mechanisms are most probably involved. Cross-linking Fc gamma RI or Fc gamma RII but not binding of the mAb to the Fc gamma R on monocytes activated phospholipase C, as demonstrated by the increase in the intracellular concentration of inositol-(1,4,5)-triphosphate. The enhanced intracellular killing stimulated by cross-linking Fc gamma R on monocytes was completely blocked by U-73122, an inhibitor of phospholipase C-dependent processes. Protein kinase C activity, but not the rise in the cytosolic free Ca++ concentration or pertussis toxin-sensitive G proteins, is essential for the Fc gamma R-mediated intracellular killing of bacteria by monocytes. Together, these results demonstrate that cross-linking Fc gamma RI or Fc gamma RII is equally effective in stimulating the intracellular killing of bacteria by monocytes and that this stimulation is a phospholipase C-dependent process.

Purification and immunological analysis of phospholipase D from castor bean endosperm

Phospholipase D (EC 3.1.4.4) has been implicated in diverse cellular processes, but its physiological role is not well established in plants. In order to develop immunological and molecular biology approaches to address the problem, we report here the immunological analysis and N-terminal amino acid sequence of a cytosolic phospholipase D from castor bean (Ricinus communis L.). The enzyme was purified to apparent homogeneity from germinating castor bean endosperm. The specific activity of the purified enzyme was enhanced by approximately 670-fold with an overall yield of 4%. Its molecular mass was estimated at 92 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The N-terminal amino acid sequence of this enzyme was KLVENIEETVGFGKG. Polyclonal antibodies were raised against the purified enzyme. The antibodies inhibited the activity of transphosphatidylation more than that of hydrolysis of phospholipase D. The differential effect on the two activities of this enzyme implies that different active sites on this enzyme may be involved in the two reactions. Immunoblot analyses showed that the amounts of phospholipase D protein relative to the total endosperm proteins increased during the first 5 days of germination. The antibodies cross-reacted to proteins from several tested plant species, and those proteins had molecular masses similar to that of castor bean phospholipase D. These results indicate that the expression of phospholipase D in castor bean changes according to growth stages and that phospholipase D enzymes of different plant species are structurally related.

Fiber-compressed high-repetition-rate pulses from a mode-locked GaAs diode laser

A GaAs diode laser (wavelength 800 nm) was actively mode locked in an external cavity that utilized grating feedback or injection seeding to control the optical spectrum of the pulses and hence the laser's frequency chirp. The chirp was large enough and the pulse duration short enough that the pulses could be compressed in single-mode optical fiber. The shortest pulses were compressed to 7 ps at a 4.1-GHz repetition rate in 550 m of optical fiber, with an average output power of 0.3 mW measured after the pulse compressor.

A detailed genetic map for the X chromosome of the malaria vector, Anopheles gambiae

Anopheles gambiae, the primary vector of human malaria in Africa, is responsible for approximately a million deaths per year, mostly of children. Despite its significance in disease transmission, this mosquito has not been studied extensively by genetic or molecular techniques. To facilitate studies on this vector, a genetic map has been developed that covers the X chromosome at an average resolution of 2 centimorgans. This map has been integrated with the chromosome banding pattern and used to localize a recessive, sex-linked mutation (white eye) to within 1 centimorgan of flanking markers.

Cysteine desulfurase activity indicates a role for NIFS in metallocluster biosynthesis

Biological nitrogen fixation is catalyzed by nitrogenase, a complex metalloenzyme composed of two separately purifiable component proteins encoded by the structural genes nifH, nifD, and nifK. Deletion of the Azotobacter vinelandii nifS gene lowers the activities of both nitrogenase component proteins. Because both nitrogenase component proteins have metallocluster prosthetic groups that are composed of iron- and sulfur-containing cores, this result indicated that the nifS gene product could be involved in the mobilization of the iron or sulfur required for metallocluster formation. In the present work, it is shown that NIFS is a pyridoxal phosphate-containing homodimer that catalyzes the formation of L-alanine and elemental sulfur by using L-cysteine as substrate. NIFS activity is extremely sensitive to thiol-specific alkylating reagents, which indicates the participation of a cysteinyl thiolate at the active site. Based on these results we propose that an enzyme-bound cysteinyl persulfide that requires the release of the sulfur from the substrate L-cysteine for its formation ultimately provides the inorganic sulfide required for nitrogenase metallocluster formation. The recent discovery of nifS-like genes in non-nitrogen-fixing organisms also raises the possibility that the reaction catalyzed by NIFS represents a universal mechanism that involves pyridoxal phosphate chemistry, in the mobilization of the sulfur required for metallocluster formation.

DNA splicing by an active site mutant of Flp recombinase. Possible catalytic cooperativity between the inactive protein and its DNA substrate

Each strand transfer catalyzed by the Flp recombinase is the composite of two transesterification reactions. The active nucleophilic species in the two reactions are the catalytic site tyrosine (Tyr-343) of Flp and the 5'-hydroxyl from the Flp-nicked DNA substrate, respectively. A "half recombination site" is capable of undergoing this pair of transesterifications in the presence of Flp. When the substrate is a half-site containing a chiral phosphorothioate at the exchange point, the Flp reaction yields a product in which the phosphate chirality is retained. A mutant of Flp that lacks the active site tyrosine, Flp(Y343F), is incapable of mediating strand transfer in a full-recombination site but can execute strand transfer in a half-site. The efficiency of this reaction is about 2% of that of the wild type reaction. The activity of Flp(Y343F) is critically dependent on the length of the half-site spacer. Furthermore, in this reaction, the strand cleavage and strand exchange steps cannot be uncoupled. These results strongly suggest a direct attack by the 5'-hydroxyl of the half-site spacer on the phosphodiester at the normal strand transfer point.

Binding of cytosolic aconitase to the iron responsive element of porcine mitochondrial aconitase mRNA

The 5' end of porcine mitochondrial aconitase mRNA contains an iron responsive element (IRE)-like secondary structure (T. Dandekar, R. Stripecke, N. K. Gray, B. Goosen, A. Constable, H. E. Johansson, and M. W. Hentze (1991) EMBO J. 10, 1903-1909). A protein from a liver extract binds to a mitochondrial aconitase RNA probe and supports the identification of this sequence as an IRE. Purified cytosolic aconitase but not the mitochondrial enzyme binds to this IRE as well as to a ferritin IRE. All forms of cytosolic aconitase, [4Fe-4S] enzyme, [3Fe-4S] enzyme and apoenzyme bind with similar affinity. A Kd of 0.25 nM was calculated for the apoaconitase-IRE interaction from Scatchard analysis. These results support the conclusion that cytosolic aconitase is an IRE-binding protein which may regulate translation of mitochondrial aconitase mRNA.

A case-control study of dietary factors in patients with lung cancer

A case-control study was designed to investigate association of dietary factors with the risk of lung cancer in Sichuan, China. The cases consisted of 135 patients with preinvasive lung cancer which had been confirmed with histopathology, fiber bronchoscope, CT and X-ray film in three provincial hospitals in the recent one year. Controls were healthy subjects who went to one of these hospitals for health check-up; patients with pulmonary diseases was excluded. Controls were matched to cases for sex and age with a ratio of 1:1. Nutrient intakes, the eating habit and other relevant factors were investigated. The data analyzed with the conditional logistic regression model indicated that dietary beta-carotene intakes had a significantly inverse association with the risk of lung cancer. Vitamin C had a less significantly inverse association with the risk. Association of protein, fat, energy, retinol intakes or diet-balance index with the risk was not significant. Association of tea, alcohol, garlic or mushroom, respectively, with the risk was also not observed. Consumption of more processed foods and deep-fried foods were found to be risk factors. Smoking and air pollution from coal burning stoves were also observed as independent risk factors of lung cancer in the present study. The mental stress incidence in the case was significantly higher than that in the control.

The beta subunit of tomato fruit polygalacturonase isoenzyme 1: isolation, characterization, and identification of unique structural features

We have purified and isolated cDNAs encoding the beta subunit of tomato fruit polygalacturonase isoenzyme 1 (PG1), a cell wall protein that associates with, and apparently regulates, the catalytic PG2 polypeptides. Expression of the beta subunit is fruit specific and temporally separated from the expression of PG2 during fruit development. The 37- to 39-kD beta subunit is encoded as a 69-kD precursor protein containing a signal sequence and two propeptide domains. The mature protein is composed almost entirely of the novel 14-amino acid motif FTNYGxxGNGGxxx in which many of the phenylalanine residues are post-translationally modified. The unique structural features of the motif suggest an important role in the function of the protein and hence in the activity of PG1. The beta subunit may represent a class of bifunctional plant proteins that interact both with structural components of the cell wall and catalytic proteins to localize and/or regulate metabolic activities within the cell wall.

Sporulation regulatory protein GerE from Bacillus subtilis binds to and can activate or repress transcription from promoters for mother-cell-specific genes

The mother-cell line of gene expression during sporulation in Bacillus subtilis is a hierarchical cascade consisting of at least four temporally controlled gene sets, the first three of which each contain a regulatory gene for the next gene set in the pathway. gerE, a member of the penultimate gene set, is a regulatory gene whose products is required for the transcriptional activation of genes (coat protein genes cotB and cotC) in the last gene set. The gerE product also influences the expression of other members of the penultimate gene set (coat protein genes cotA and cotD appear to be repressed and activated, respectively). We now report that the purified product of gerE (GerE) is a DNA-binding protein that adheres to the promoters for cotB and cotC. We also show that GerE stimulates cotB and cotC transcription in vitro by RNA polymerase containing the mother-cell sigma factor sigma K. These findings support the view that GerE is a positively acting, regulatory protein whose appearance at a late stage of development directly activates the transcription of genes in the last known temporal class of mother-cell-expressed genes. In addition, GerE stimulates cotD transcription and inhibits cotA transcription in vitro by sigma K RNA polymerase, as expected from in vivo studies, and, unexpectedly, profoundly inhibits in vitro transcription of the gene (sigK) that encodes sigma K. The effects of GerE on cotD and sigK transcription are just the opposite of the effects exerted by the earlier-appearing, mother-cell regulatory protein spoIIID, suggesting that the ordered appearance of first SpoIIID, then GerE, ensures proper flow of the regulatory cascade controlling gene expression in the mother cell.

Gonadotropin-releasing hormone-induced calcium signaling in clonal pituitary gonadotrophs

In agonist-stimulated clonal pituitary gonadotrophs (alpha T3-1 cells), cytoplasmic calcium ([Ca2+]i) exhibited rapid and prominent peak increases, followed by lower, but sustained, elevations for up to 15 min. The [Ca2+]i response to GnRH was rapidly inhibited by prior addition of a potent GnRH antagonist. In the absence of extracellular Ca2+ the initial peak [Ca2+]i response was only slightly decreased, but the prolonged increase in [Ca2+]i was abolished, indicating that the peak is derived largely from intracellular calcium mobilization and the sustained phase from Ca2+ influx. Application of the endoplasmic reticulum Ca(2+)-ATPase blocker thapsigargin caused progressive and dose-dependent elevation of [Ca2+]i and decreased the peak amplitude of the GnRH-induced Ca2+ response. On the other hand, addition of dihydropyridine calcium channel antagonists before or after GnRH treatment prevented or terminated the plateau phase, respectively, consistent with entry of Ca2+ through L-type voltage-sensitive Ca2+ channels (VSCC) as the major Ca2+ influx pathway during GnRH action. The presence of L-type VSCC in alpha T3-1 cells was further indicated by the ability of elevated extracellular K+ levels and the dihydropyridine calcium channel agonist Bay K 8644 to elevate [Ca2+]i in an extracellular calcium-dependent manner. These actions of depolarization and Bay K 8644 were inhibited by nifedipine, with an IC50 of 10 nM. High extracellular K(+)- and GnRH-induced Ca2+ entry was also attenuated by phorbol esters and permeant diacylglycerols, indicating that protein kinase-C exerts inhibitory modulation of VSCC activity. In contrast to normal pituitary gonadotrophs, in which GnRH induces a frequency-modulated oscillatory [Ca2+]i response, single alpha T3-1 cells exhibited a nonoscillatory amplitude-modulated signal during agonist stimulation. The [Ca2+]i responses observed in alpha T3-1 gonadotrophs indicate that the immortalized cells retain functional GnRH receptors and their coupling to the Ca2+ signaling pathway. Ca2+ influx through L-type channels maintains the plateau phase of the [Ca2+]i response during agonist stimulation and is inhibited by activation of protein kinase-C.