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.

Cytosolic free calcium is essential for immunoglobulin G-stimulated intracellular killing of Staphylococcus aureus by human monocytes

Earlier studies have shown that the intracellular killing of Staphylococcus aureus by human monocytes requires continuous stimulation by serum factors, e.g., immunoglobulin G (IgG). In the present study, we demonstrate that IgG, at concentrations that stimulate the intracellular killing of S. aureus, induces a transient increase in the intracellular free calcium concentration ([Ca2+]i) in monocytes. The Ca2+ ionophores A23187 and ionomycin stimulate the killing process as efficiently as IgG does and initiate O2- production in resting monocytes but not in monocytes containing bacteria. The Ca2+ ionophore-stimulated killing process was markedly inhibited by the NADPH oxidase inhibitor diphenyleneiodonium bisulfate, which indicates that these ionophores stimulate oxygen-dependent bactericidal mechanisms. Reduction of the [Ca2+]i to values below 1 nM, obtained by loading monocytes with MAPT/AM (1,2-bis-5-methyl-aminophenoxylethane-N,N,N',N'-tetraacetoxymet hyl acetate) in the absence of extracellular Ca2+, rendered the cells unresponsive to IgG or Ca2+ ionophore stimulation of the intracellular killing of S. aureus, but the response could be restored by reincubating these cells in the presence of extracellular Ca2+. It is concluded that cytosolic free Ca2+ is essential for the IgG-stimulated intracellular killing of S. aureus by human monocytes.

[Determination of cinnamaldehyde in cortex Cinnamomi by CS-930 TLC scanner]

Cinnamaldehyde was extracted by chloroform from Cortex Cinnamomi and determined directly on a CS-930 TLC scanner. The method is simple and sensitive, and can serve as an index for checking the quality of Cortex Cinnamomi.

Mutational analysis of active site residues in pig heart aconitase

A cDNA encoding mature porcine heart aconitase was over-expressed in Escherichia coli under the control of a phage T7 promoter. Recombinant aconitase purified from E. coli was identical to the enzyme from pig and beef heart in size, [3Fe-4S] and [4Fe-4S] cluster structure and enzymatic activity. Nine amino acid residues in close proximity to the Fe-S cluster and bound substrate (Lauble, H., Kennedy, M.C., Beinert, H., and Stout, C.D. (1992) Biochemistry, in press) were replaced by site-directed mutagenesis. Fe-S cluster environment as indicated by the EPR spectrum, tight binding of substrate, and enzymatic activity were compared for the mutant and wild type enzymes. Significant perturbations were detected for all of the mutant enzymes. Replacements for Asp100, His101, Asp165, Arg580, and Ser642 result in a 10(3)-10(5)-fold drop in activity, which suggests that these residues are involved in critical aspects of the reaction. Arg580 appears to be a key residue for substrate binding, as shown by a 30-fold increased Km and loss of tight substrate binding. Results of mutagenesis support the interpretation of the x-ray model, namely that Asp100 and His101 form an ion pair for elimination of the substrate hydroxyl and Ser642 may function as a general base for proton abstraction from citrate or isocitrate in the dehydration step and protonation of cis-aconitate in the hydration step. Asp165 appears to play a critical role in the interaction of Fea with substrate.

[Short-term effect and the mechanism of radix Angelicae on pulmonary hypertension in chronic obstructive pulmonary disease]

The changes of hemodynamics, hemorheology and blood gas were investigated in 28 stable COPD patients with pulmonary hypertension after short-term treatment by Radix Angelicae. The level of TXA2, PGI2 were measured in 10 of the 28 patients before and after treatment. The results show that Radix Angelicae produced significant improvement on pulmonary hypertension, blood viscosity, hematocrit and the level of TXA2 decreased significantly. But the blood gas, blood pressure and the level of PGI2 remained unchanged in all of the patients.

NMR studies of retinal proteins

A review is given of the use of nuclear magnetic resonance (NMR) spectroscopy to study bacteriorhodopsin and bovine rhodopsin. Solution and solid-state approaches are included. The studies of the bacterial proton pump examine the chromophore, the peptide backbone, and the protein side chains. The studies of the bovine visual pigment are limited to the chromophore. Various forms of each pigment are considered. Both structural and dynamic features are addressed.

Purification and N-terminal amino acid sequences of two polypeptides encoded by the mcrB gene from Escherichia coli K-12

This report provides a purification method for the two proteins, 51 kDa and 33 kDa, both encoded by the same mcrB gene of the McrBC restriction system in Escherichia coli K-12. The two proteins were produced in large quantity using a T7 expression system and copurified to near homogeneity by DEAE-Sepharose and Affi-Gel blue column chromatography. The N-terminal amino acid sequences of these purified McrB proteins were the same as those predicted from the mcrB DNA sequence by Ross et al. [J. Bacteriol. 171 (1989b) 1974-1981]. The 33-kDa protein totally overlaps the C-terminal part of the 51-kDa protein.

[Volatile oil in Ephedra sinica Stapf. and its processed products by GC-MS]

This paper deals with the changes in contents and chemical composition in the volatile oil of Ephedra sinica before and after processing. The results indicate that after processing, the more the substances of low boiling point, the higher their contents and vice versa. The changes are particularly obvious in yellow-fried Ephedra sinica.

Seasonal variation of cerebral hemorrhage in 236 consecutive cases in Brussels

BACKGROUND AND PURPOSE

Seasonal variation in the incidence of cerebral hemorrhage has been previously demonstrated. In this study, we sought to identify the climatological data best correlated with this seasonal variation.

METHODS

In a retrospectively studied sequential series of 236 patients with nontraumatic cerebral hemorrhage observed in Brussels over a period of 8 years, we cumulatively grouped the dates of stroke occurrence into a single calendar year.

RESULTS

We found marked seasonal variation in incidence, with the highest value (23%) observed in November-December and the lowest (10%) in July-August. Seasonal variations in incidence of cerebral hemorrhage were shown to be correlated not only with the inverse of ambient temperature, but also with the inverse of hours of sunshine and with ambient humidity. We found no difference between hypertensive and normotensive patients.

CONCLUSIONS

Our study fails to bear out the hypothesis that the higher incidence of cerebral hemorrhage in late autumn and winter is due to the influence of low ambient temperature on blood pressure.

Low-resolution genome map of the malaria mosquito Anopheles gambiae

We have microdissected divisions of the Anopheles gambiae polytene chromosomes, digested the DNAs with a restriction enzyme, and PCR-amplified the DNA fragments to generate a set of pooled probes, each corresponding to approximately 2% of the mosquito genome. These divisional probes were shown to have high complexity. Except for those derived from near the centromeres, they hybridize specifically with their chromosomal sites of origin. Thus, they can be used to map cloned DNAs by a dot blot procedure, which is much more convenient than in situ hybridization to polytene chromosomes. We discuss additional potential uses of these probes, such as easier isolation of molecular markers and genes, including those that cross-hybridize with clones available from other insects. It is expected that the probes will substantially accelerate molecular genetic analysis of this most important malaria vector.

Overproduction and purification of McrC protein from Escherichia coli K-12

The McrC protein, encoded by one of the two genes involved in the McrB restriction system, was produced in Escherichia coli cells by using a T7 expression system. Following sequential DEAE-Sepharose and hydroxylapatite column chromatography, the protein was purified to apparent homogeneity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The N-terminal amino acid sequence of the purified McrC protein agreed exactly with the one deduced from the DNA sequence by Ross et al. (J. Bacteriol. 171:1974-1981, 1989).

Tyr60 variants of Flp recombinase generate conformationally altered protein-DNA complexes. Differential activity in full-site and half-site recombinations

The tyrosine at position 60 of the Flp recombinase of the Saccharomyces cerevisiae plasmid, 2 mu circle, is invariant among site-specific recombinases of the "yeast plasmid family". Alterations of this residue give rise to Flp variants that show no recombination activity when assayed in vivo in Escherichia coli. Upon purification, they bind substrate, execute DNA cleavage and catalyze recombination. The efficiency of strand cleavage follows the order: Flp(Y60F) greater than Flp greater than Flp(Y60S) greater than Flp(Y60D); efficiency of recombination between Flp sites on a linear substrate and a circular one follows the order: Flp greater than Flp(Y60F) greater than Flp(Y60S) greater than Flp(Y60D). Methylation footprints of the DNA-protein complexes formed by two of the Flp variants, Flp(Y60S) and Flp(Y60D), do not show hypermethylation of the G residues within the substrate core that is characteristic of complexes formed by wild-type Flp. The third variant, Flp(Y60F), causes significant distortion (although less than wild-type Flp) of the substrate core, as indicated by enhanced G-methylation. Binding profiles with circularly permuted substrates indicate that Flp(Y60S) and Flp(Y60D), but not Flp(Y60F), are defective in bending substrate DNA. In recombination between two Flp half-sites, the variant proteins are significantly more active than in normal full-site recombination.

[Changes of thromboxane A2 (TXA2) and prostacyclin (PGI2) in COPD patients with pulmonary hypertension]

We measured the pulmonary arterial pressure and the level of Thromboxane A2 (TXA2), and Prostacyclin (PGI2) in 30 stable COPD patients and the level of TXA2 and PGI2 in 10 normal subjects so as to investigate the changes of TXA2 and PGI2 in COPD patients with pulmonary hypertension. The results showed that the level of TXA2 increased significantly in COPD patients with dominant and latent pulmonary hypertension when compared with that in normal subjects (P less than 0.001, less than 0.01), and the level of TXA2 in COPD patients with dominant pulmonary hypertension was also higher than that in COPD patients with latent pulmonary hypertension (P less than 0.02), but there was no difference in the level of PGI2 among normal subjects and COPD patients with or without pulmonary hypertension. This indicates that TXA2 plays an important role in causing pulmonary hypertension in COPD patients.

Functional analysis of Arg-308 mutants of Flp recombinase. Possible role of Arg-308 in coupling substrate binding to catalysis

The arginine residue at position 308 in the Flp recombinase corresponds to the only invariant arginine within the Int family of recombinases. Alterations of this residue result in Flp variants that retain substrate recognition, but form weaker protein-DNA complexes than wild type Flp. Furthermore, their DNA cleavage activity is significantly diminished. A conservative change of R308K results in a functional Flp variant; however, this protein has a lowered temperature optimum for recombination. The Arg-308 mutants can be stabilized on the DNA substrate through cooperativity with a partner Flp mutant that is tight binding. Thus, interactions between Flp monomers must be a relevant feature of the normal recombination reaction.

Cloning and structural characterization of porcine heart aconitase

A full-length cDNA encoding porcine heart aconitase was derived from lambda gt10 recombinant clones and by amplification of the 5' end of the mRNA. The 2700-base pair (bp) cDNA contains a 29-bp 5' untranslated region, a 2343-bp coding segment, and a 327-bp 3' untranslated region. The porcine heart enzyme is synthesized as a precursor containing a mitochondrial targeting sequence of 27 amino acid residues which is cleaved to yield a mature enzyme of 754 amino acids, Mr = 82,754, having a blocked amino terminus. The NH2-terminal pyroglutamyl residue of the mature enzyme was identified by fast atom bombardment mass spectrometry and sequence analyses of an NH2-terminal peptide. Mature porcine heart aconitase contains 12 cysteine residues. Cysteines 358, 421, and 424 are ligands to the Fe-S cluster in the inactive [3Fe-4S] (Robbins, A. H., and Stout, C. D. (1989) Proteins 5, 289-312) and active [4Fe-4S] (Robbins, A. H., and Stout, C. D. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 3639-3643) forms. An alignment of the derived porcine heart sequence with 8 cysteine-containing tryptic peptides from bovine heart aconitase (Plant, D. W., and Howard, J. B. (1988) J. Biol. Chem. 263, 8184-8189; Plank, D. W., Kennedy, M. C., Beinert, H., and Howard, J. B. (1989) J. Biol. Chem. 264, 20385-20393) shows that 198 of 202 amino acids are conserved and suggests that the two enzymes are virtually identical.