Differentiation among spotted fever group rickettsiae species by analysis of restriction fragment length polymorphism of PCR-amplified DNA

Restriction fragment length polymorphism (RFLP) analysis of PCR-amplified genes was used to study spotted fever group (SFG) rickettsiae, extending the previous work of Regnery et al. (R.L. Regnery, C.L. Spruill, and B.D. Plikaytis, J. Bacteriol. 173:1576-1589, 1991). Twenty-six strains of SFG rickettsia were studied, including several recognized species which have never been studied (R. parkeri, R. helvetica, and R. japonica) as well as strains which are not currently classified. Two previously used primer pairs derived from the R. prowazekii citrate syntase gene and the R. rickettsii 190-kDa protein antigen gene were studied, as were primer pairs obtained from the R. rickettsii 120-kDa protein antigen gene. By using three amplifications and three enzyme digestions, it was possible to differentiate between almost all of the known SFG rickettsia species and to differentiate between several strains of the R. conorii complex. Two human pathogens, "R. africae" and the Israeli tick typhus rickettsia, were first separated by using BG-12 pair primer amplification and then RsaI restriction endonuclease digestion. The proposed simplified model of identification may be useful in studying the geographical distributions of SFG rickettsiae.

Bidirectional modulation of GABA-gated chloride channels by divalent cations: inhibition by Ca2+ and enhancement by Mg2+

The effects of the divalent cations Ca2+, Sr2+, Ba2+, Mg2+, Mn2+, and Cd2+ were studied on gamma-aminobutyric acidA (GABAA) responses in rat cerebral cortical synaptoneurosomes. The divalent cations produced bidirectional modulation of muscimol-induced 36Cl- uptake consistent with their ability to permeate and block Ca2+ channels. The order of potency for inhibition of muscimol responses was Ca2+ > Sr2+ > Ba2+, similar to the order for permeation of Ca2+ channels in neurons. The order of potency for enhancement of muscimol responses was Cd2+ > Mn2+ > Mg2+, similar to the order for blockade of Ca2+ channels in neurons. Neither Ca2+ nor Mg2+ caused accumulation of GABA in the extravesicular space due to increased GABA release or decreased reuptake of GABA by the synaptoneurosomes. The inhibition of muscimol responses by Ca2+ was most likely via an intracellular site of action because additional inhibition could be obtained in the presence of the Ca2+ ionophore, A23187. This confirms electrophysiologic findings in cultured neurons from several species. In contrast, the effects of Cd2+, Mn2+, and Mg2+ may be mediated via blockade of Ca2+ channels or by intracellular sites, although the results of these studies do not distinguish between the two loci. The effects of Zn2+ were also studied, because this divalent cation is reported to have widely divergent effects on GABAA responses. In contrast to other studies, we demonstrate that Zn2+ inhibits GABAA responses in an adult neuronal preparation. Zn2+ produced a concentration-dependent inhibition (limited to 40%) of muscimol responses with an EC50 of 60 microM. The inhibition of muscimol-induced 36Cl- uptake by Zn2+ was noncompetitive.(ABSTRACT TRUNCATED AT 250 WORDS)

Three-dimensional reconstruction of a co-complex of F-actin with antibody Fab fragments to actin's NH2 terminus

We have decorated F-actin with Fab fragments of antibodies to actin residues 1-7. These antibody fragments do not strongly affect the rigor binding of myosin S-1 to actin, but do affect the binding of S-1 to actin in the presence of nucleotide (DasGupta, G., and E. Reisler, 1989. J. Mol. Biol. 207:833-836; 1991. Biochemistry. 30:9961-9966; 1992. Biochemistry. 31:1836-1841). Although the binding constant is rather low, we estimate that we have achieved about 85% occupancy of the actin sites. Three-dimensional reconstructions from electron micrographs of both negatively stained and frozen-hydrated filaments show that the Fab fragment is bound at the location of the NH2 terminus in the model of Holmes et al. (Holmes, K.C., D. Popp, W. Gebhard, and W. Kabsch. 1990. Nature. 347:37-44) for F-actin, excluding very different orientations of the actin subunit in the filament. Most of the mass of the antibody is not visualized, which is due to the large mobility of the NH2 terminus in F-actin, differences in binding angle within the polyclonal antibody population, or a combination of both of these possibilities.

Characterization and regulation of the protein binding to a cis-acting element, RET 1, in the rat opsin promoter

RET 1 is a binding site for retinal nuclear proteins located at -136 to -110 bp in the rat opsin promoter, as defined by DNase protection assays. A similar sequence is found in the upstream flanking regions of many other photoreceptor genes in mammals and other species, including Drosophila. A 7-base consensus sequence, CAATTAG, is found in these genes and has the binding activity of the longer RET 1 element. A 40-kDa protein that binds to RET 1 has been purified over 2 x 10(5)-fold to apparent homogeneity by affinity chromatography. The RET 1 binding activity is first detectable at E18 and increases during the first two postnatal weels, At embryonic ages the retarded bands show an altered mobility and at early postnatal ages two bands are detected, with the adult band increasing and the embryonic band decreasing in intensity. Treatment of early postnatal retinas with bFGF increased the binding activity in nuclear extracts and caused a shift in migration of the retarded band to a position characteristic of the embryonic form of the complex. The results support the hypothesis that RET 1-like elements play an important role in rod photoreceptor development.

A cis-acting element, T alpha-1, in the upstream region of rod alpha-transducin gene that binds a developmentally regulated retina-specific nuclear factor

The G protein transducin (T) is an integral component of the signal transduction pathway in photoreceptors. We have identified a cis-acting element, T alpha-1, in the upstream region of the mouse rod alpha-T (Tr alpha) gene that may be important for tissue-specific expression. T alpha-1 binds a retina-specific nuclear factor of apparent molecular mass of 90 kDa. Binding to the T alpha-1 site is developmentally regulated and peaks between postnatal days 6 and 9. This corresponds to the time of rod photoreceptor maturation and the rise in Tr alpha gene expression. The sequence of T alpha-1 shows homology with RET-1, a cis-acting element in the proximal promoter of opsin gene that binds a distinct retina-specific factor. T alpha-1 and RET-1 sequences may have been derived from a prototype T alpha-1/RET-1 sequence, evolved to confer photoreceptor specificity on retina-specific genes.

Detection of Ehrlichia chaffeensis in human tissue by using a species-specific monoclonal antibody

A mouse monoclonal antibody (MAb 1A9) was produced and used in detection of Ehrlichia chaffeensis in human tissues including kidney, liver, and lung by using an indirect immunohistologic stain. MAb 1A9 was specific to E. chaffeensis and did not react with other bacteria, including Ehrlichia canis, which is the organism most closely related to E. chaffeensis. It reacted with an epitope present in two surface proteins of E. chaffeensis with molecular masses of 29 and 27 kDa. E. chaffeensis was easily detected in human tissue by immunohistology with MAb 1A9. This study demonstrates that our MAb can provide a specific and simple method for detection of E. chaffeensis in clinical specimens for establishing an etiologic diagnosis of human ehrlichiosis; it may also provide a tool for the investigation of immunopathologic characteristics in infected patients.

Regulation of Defense-related Gene Expression during Plant-Pathogen Interactions

Plants have evolved a broad array of defense mechanisms involved in disease resistance. These include synthesis of phytoalexin antibiotics and proteinase inhibitors, deposition of cell wall materials, and accumulation of hydrolytic enzymes such as chitinases. Resistance appears to depend on the ability of the host to recognize the pathogen rapidly and induce these defense responses in order to limit pathogen spread. Application of molecular technologies has yielded significant new information on mechanisms involved in pathogen recognition, signal transduction, and defense-related gene activation, and is leading to novel strategies for engineering enhanced disease resistance. We are using these approaches to analyze regulation of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR), a key enzyme mediating the production of terpenoid defense compounds. This enzyme is encoded by four genes in tomato; hmg2 gene expression is specifically associated with responses to pathogen or defense elicitors. Transgenic plants containing DNA constructs that fuse the hmg2 promoter to a reporter gene have been used to analyze both tissue specificity and patterns of defense-related expression. Because this gene is rapidly induced in tissues directly surrounding the site of ingress by a variety of pathogens, it may serve as a valuable tool in engineering new disease-resistance mechanisms.

Functional reconstitution of drug transport and ATPase activity in proteoliposomes containing partially purified P-glycoprotein

P-glycoprotein, the multidrug transporter, is proposed to act as an ATP-driven drug efflux pump. We previously reported the partial purification of P-glycoprotein from multidrug-resistant cells (Doige, C. A., Yu, X., and Sharom, F. J. (1992) Biochim. Biophys. Acta 1109, 149-160). We now report the reconstitution of this preparation into phospholipid bilayers using rapid detergent removal by gel filtration chromatography. The resulting proteoliposomes displayed ATP-dependent [3H]colchicine uptake over a time period of 0-4 min. No drug uptake was observed for liposomes of lipid alone, or liposomes reconstituted with a similar extract from drug-sensitive cells. Drug uptake was osmotically sensitive, and abolished by detergent permeabilization, indicating that it represented true transport into the vesicle lumen. Steady-state levels of drug uptake increased with drug concentration, approaching saturation at approximately 150 microM colchicine, with half-maximal accumulation at 50 microM. Drug was accumulated actively against a 5.6-fold concentration gradient. Multidrug resistance spectrum drugs and chemosensitizers inhibited colchicine uptake by P-glycoprotein proteoliposomes, whereas cytosine arabinoside and methotrexate had no effect. Reconstituted liposomes showed high levels of ATPase activity, which was stimulated over 2-fold by verapamil and trifluoperazine. These results suggest that P-glycoprotein functions as an active drug transporter with constitutive ATPase activity.

Expression of monocyte chemoattractant protein 1 in human inflamed gingival tissues

Gingival inflammation is initiated by bacterial colonization on the tooth surface. It is characterized by infiltration of mononuclear cells, a common feature of many forms of chronic inflammation. Monocyte chemoattractant protein 1 (MCP-1) is the predominant monocyte chemoattractant secreted by a variety of different cells in vitro. For this report, we examined MCP-1 expression in bacterially induced gingival inflammation by immunohistochemistry and in situ hybridization. The cell types expressing MCP-1 are identified as vascular endothelial cells and monocytes/macrophages. Correlation analysis shows that the number of cells expressing MCP-1 is related to the degree of inflammation. Our finding that MCP-1 is expressed in inflamed gingival tissue suggests that MCP-1 plays an important role in the recruitment of monocytes and amplification of inflammatory signals in bacterially induced inflammation.

Mutations in the N-terminal region of human immunodeficiency virus type 1 matrix protein block intracellular transport of the Gag precursor

The matrix domain of human immunodeficiency virus type 1 Gag polyprotein was studied for its role in virus assembly. Deletion and substitution mutations caused a dramatic reduction in virus production. Mutant Gag polyproteins were myristoylated and had a high affinity for membrane association. Immunofluorescence staining revealed a large accumulation of mutant Gag precursors in the cytoplasm, while wild-type Gag proteins were primarily associated with the cell surface membrane. These results suggest a defect in intracellular transport of the mutant Gag precursors. Thus, in addition to myristoylation, the N-terminal region of the matrix domain is involved in determining Gag protein transport to the plasma membrane. Wild-type Gag polyproteins interacted with and efficiently packaged mutant Gag into virions. This finding is consistent with the hypothesis that intermolecular interaction of Gag polyproteins might occur in the cytoplasm prior to being transported to the assembly site on the plasma membrane.

Dentin bonding system shelf life and bond strength

The purpose of this study was to assess the shelf life of dentin bonding systems by means of bond strength testing. The systems evaluated were Mirage-Bond, All-Bond and Tenure. Specimens were tested immediately, and 1, 2, 3, 4, 5 and 12 months after opening the kits. Flat dentin surfaces were created on 210 extracted human molars that had been stored in saline. Ten specimens were prepared for each dentin bonding system at each shelf time. Each material was prepared and placed following the manufacturer's instructions. Prisma MicroFine resin composite was then placed. Shear bond strength testing was conducted using a universal testing machine. A two-way ANOVA indicated a significant interaction between bonding system and storage time (F = 2.28, P = 0.01). Multiple comparison tests indicated statistically significant bond strength differences by storage time for All-Bond and Mirage-Bond. In addition, a comparison of bonding systems at each storage time revealed significant differences at three of the seven times. These results suggest that shelf life for two of the three dentin bonding systems may be significantly shorter than currently presumed.

Sustained root culture for generation and vegetative propagation of transgenic Arabidopsis thaliana

Excised roots of wild-type and nitrate-reductase deficient mutant Arabidopsis thaliana (L.) HEYNH. can be propagated as sustained root cultures in liquid medium. Culture initiation from a single seedling required a two-day indoleacetic acid treatment at 0.05 mg/l concentration. Indoleacetic acid facilitated subculture but was not essential for sustained growth. This procedure has allowed the clonal propagation of roots derived from individual wildtype and mutant seedlings for more than 21 months. The cultured roots retained their shoot regeneration ability; however, a controlled desiccation treatment was required to restore it to the level of freshly excised roots. The chromosome number remained diploid and no evidence for the accumulation of recessive mutations was observed. The cultured roots are competent for Agrobacterium-mediated transformation. The sustained root culture technology allowed the maintenance of transgenic tissues in which expression of a dominant, seed-lethal gene (seed-specific pea vicilin promoter fused to diphtheria toxin A chain gene) precluded generative propagation.

Protective effect of Salmonella typhimurium Re-LPS antiserum

There is increasing evidence that antiserum to LPS can reduce the morbidity and mortality of Gram-negative bacterial infections. We report that antiserum to S. typhimurium SL 1102 (Re mutant strain) has excellent cross-protective activity. Antisera to these bacteria and to their Re-LPS were prepared in rabbits immunized with heat-killed bacterial cells and with Re-LPS preparations. Re-LPS antibody titers were tested by immune hemagglutination (IHA) and by ELISA. These antisera were found to be capable of protecting ICR mice against lethal challenge with S-type S. typhimurium 50014 (100 LD50), E. coli 0111:B4 (32 LD50), Pseudomonas aeruginosa (8 LD50) and Klebsiella pneumonia (16 LD50). We used gastric mucin (5%) as a virulence enhancing agent for the bacterial challenges. The IHA titer of antibody to the homologous strain proved to be much higher than that of other strains. Protection by the sera was 75-100%, 25% and 0% when injected 24, 48 or 72 h before the challenge, respectively. The survival rate was more than 50% when the antiserum was injected 5-7 h after challenge with a ten-fold or higher lethal dose. No protection was observed against such high challenge when the serum was injected later. According to these results, Re-LPS antiserum provides better protection than S-type specific antisera.

Effects of anions on the Ca2+, H+ and electrical gradients formed by the sarcoplasmic reticulum ATPase in reconstituted proteoliposomes

The chaotropic character of several ions determines their partition on membrane interfaces with aqueous media as predicted by the Hofmeister series. However, specific characteristics of each individual ion determine its ability to cross the membrane and to influence Ca2+, H+ and electrical gradients produced by the sarcoplasmic reticulum (SR) Ca2+ pump in reconstituted proteoliposomal vesicles. Specific effects of this kind may be relevant to a variety of biological systems, including the excitation-contraction coupling of muscle fibers in which SR plays a prominent role.

DNA conformation induced by the bacteriophage T4 UvsX protein appears identical to the conformation induced by the Escherichia coli RecA protein

The study of homologous genetic recombination has been dominated by the RecA protein of Escherichia coli, which is involved in DNA recombination and repair, as well as phage induction, in vivo. The active form of the RecA protein is a helical filament formed on DNA in the presence of ATP, and within this filament, the DNA is extensively stretched to about 5.1 A rise per base-pair and untwisted to about 19 base-pairs per turn. The bacteriophage T4 UvsX protein is only weakly homologous to RecA, but it has very similar ATP-dependent DNA binding and strand-exchange activities. We can now show that the UvsX protein forms helical filaments that are very similar to those made by RecA, and induces the same extended DNA conformation within these filaments that is induced by RecA. This implies that the unusual conformation of DNA in the RecA filament may be a universal structure in homologous recombination.

Vpx of simian immunodeficiency virus is localized primarily outside the virus core in mature virions

Human immunodeficiency virus type 2 and the related simian immunodeficiency virus (SIV) contain a unique regulatory gene, vpx. The Vpx protein is packaged in mature virions and is required for efficient viral replication in peripheral blood lymphocytes and macrophages. To study the localization of Vpx in mature virions, conical and bar-shaped core structures of SIV from macaques (SIVmac) were purified. The SIVmac core has a density of approximately 1.25 g/cm3, compared with 1.16 g/cm3 for an intact virion. The relative proportions of major capsid protein (p27) and reverse transcriptase activity were similar for intact virions and core structures. The majority of matrix protein (p14) was removed from the purified core structure, suggesting its association with the viral membrane. Similarly, most of the Vpx protein was absent from the purified core structure. This result suggests that as with the matrix protein, the majority of Vpx proteins are localized outside the virus core. The localization of Vpx suggests that it may be involved in virus entry such as penetration or uncoating.

[Fermentation of engineered strain producing cholera toxin B subunit]

Studies indicate that the cholera B subunit could be synthesized efficiently in corn steep liquor by engineered E. coli strain MM2. We have also determined the optical density, pH and the yield of B subunit kinetically during fermentation. Corn steep liquor medium has advantages in low cost, simplicity in technological process and high yield of B subunit which can reaches 40 micrograms/ml in 50L fermentative tank.

Shear strength and microleakage of light-cured glass ionomers

Bond to dentin and marginal integrity of three light activated glass ionomer cements were evaluated, and compared to a traditional chemical-cured glass ionomer cement. Results indicated no significant difference in shear bond strength among the glass ionomer cements tested. However, there was a significant difference among glass ionomer cements in bond strength variability, with coefficients of variation ranging from 55 to 102%. A discrepancy between manufacturers' instructions and optimum curing times is one possible explanation for these results. There were also no significant differences in microleakage among glass ionomer cements. Most samples exhibited minimal or no microleakage.

Assessment of metals in reconstituted metallothioneins by electrospray mass spectrometry

A method has been developed that combines electrospray ionization mass spectrometry with pH control to provide analysis of metals in native or reconstituted metallothioneins. These metalloproteins cooperatively bind seven divalent metal ions, most commonly Zn2+ and Cd2+. Since the protein is denatured and metal ions are lost below pH3, the pH of the electrospray solution is critical to successful results. The metal-free apoprotein was detected with its most abundant ions in a charge state of 6+, while the folded metallothionein-metal complexes were observed with lower charge states. The retention of seven metals in the molecular ions detected is consistent with the hypothesis that metallothionein retains its conformation in the gas phase. This mass spectrometric technique can be used to determine rapidly and accurately how many and what cations are incorporated per molecule of protein. Information about molar distributions and estimates of relative abundances of various complexes in the sample can be acquired in a single measurement.

The LexA repressor binds within the deep helical groove of the activated RecA filament

The RecA protein of Escherichia coli, as a result of DNA damage, catalyzes the cleavage of its own repressor, the LexA protein, and thereby initiates the SOS response. Using a non-cleavable LexA mutant, we have obtained a co-complex of both the RecA and LexA proteins on DNA. Mass analysis using scanning transmission electron microscopy suggests that the site size of the LexA repressor on RecA is two, which would be consistent with a nearest-neighbor exclusion model for binding. Three-dimensional reconstruction of electron micrographs of these filaments shows that the LexA protein is bound in the deep groove of the RecA filament, with two strong regions of contact that span adjacent RecA protomers within the filament. One contact is consistent with a proposed LexA binding site in the RecA crystal structure. The other contact maps onto a region that has been postulated to be a second DNA-binding site within RecA, which can explain the inhibition of RecA cleavage of LexA by excess DNA.

A virion-specific inhibitory molecule with therapeutic potential for human immunodeficiency virus type 1

A potential new approach for gene therapy against human immunodeficiency virus type 1 (HIV-1) infection is the design of a nonstructural gene-based virion-specific inhibitory molecule that is packaged with virus to destroy its infectivity. We tested this approach for HIV-1 by using Vpx, a virion-associated protein of HIV-2 and simian immunodeficiency virus. Vpx was incorporated into HIV-1 virions and the resulting cell-free virus lost infectivity in CD4+ human T cells. This demonstrates the therapeutic potential of an accessory gene-based virion-specific inhibitory molecule. Vpx and its derivatives can be regarded as a new class of anti-HIV-1 molecule.