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At least 19 recordsLinked to original sources
PubMed1993

Salicylate induction of antibiotic resistance in Escherichia coli: activation of the mar operon and a mar-independent pathway.

Since the growth of wild-type Escherichia coli in salicylate results in a multiple antibiotic resistance phenotype similar to that of constitutive mutants (Mar) of the chromosomal mar locus, the effect of salicylate on the expression of the marRAB operon was investigated. The amount of RNA hybridizing with a mar-specific DNA probe was 5 to 10 times higher in wild-type cells grown with sodium salicylate (5.0 mM) than in untreated controls. Untreated Mar mutants had three to five times more mar-specific RNA than wild-type cells did. When a Mar mutant was treated with salicylate, a 30- to 50-fold increase of mar-specific RNA was seen. In wild-type cells bearing a mar promoter-lacZ fusion on the chromosome, salicylate increased beta-galactosidase activity by sixfold. Thus, salicylate induces transcription of the marRAB operon. Other inducers of phenotypic multiple antibiotic resistance, e.g., benzoate, salicyl alcohol, and acetaminophen, but not acetate, also increased transcription from the mar promoter but to a lesser extent than did salicylate. Both in wild-type and mar-deficient strains, growth in salicylate resulted in increased antibiotic resistance, decreased permeation of the outer membrane to cephaloridine, increased micF transcription, and decreased amounts of OmpF. However, the magnitude of these changes was generally greater in wild-type (mar-containing) cells. Thus, salicylate and other compounds can induce transcription of the mar operon and, presumably, give rise to multiple antibiotic resistance via this pathway. However, salicylate can also activate an unidentified, mar-independent pathway(s) which engenders multiple antibiotic resistance.

Ampicillin↗
PubMed1998

Magnetic Field and Plasma Observations at Mars: Initial Results of the Mars Global Surveyor Mission

The magnetometer and electron reflectometer investigation (MAG/ER) on the Mars Global Surveyor spacecraft has obtained magnetic field and plasma observations throughout the near-Mars environment, from beyond the influence of Mars to just above the surface (at an altitude of approximately 100 kilometers). The solar wind interaction with Mars is in many ways similar to that at Venus and at an active comet, that is, primarily an ionospheric-atmospheric interaction. No significant planetary magnetic field of global scale has been detected to date (<2 x 10(21) Gauss-cubic centimeter), but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of Mars is reported.

Journal Article↗
PubMed1997

Interaction of the nuclear matrix-associated region (MAR)-binding proteins, SATB1 and CDP/Cux, with a MAR element (L2a) in an upstream regulatory region of the mouse CD8a gene.

Matrix-associated regions (MARs), AT-rich DNA segments that have an affinity for the nuclear matrix, have been shown to play a role in transcriptional regulation of eukaryotic genes. The present study demonstrates that a DNA element, called L2a, which has been implicated in the transcriptional regulation of the mouse CD8a gene encoding an important T cell coreceptor, is a MAR. Moreover, the identities of two nuclear proteins, L2a-P1 and L2a-P2, previously shown to bind to the L2a element, have been determined. The L2a-P1 protein found to be present in all CD8-positive T cell lines tested is SATB1, a known MAR-binding protein. The widely expressed L2a-P2 protein is CDP/Cux, a MAR-binding protein that has been associated with repression of gene transcription. Interaction of both proteins with the L2a element was studied using the missing nucleoside approach, DNase I footprinting, and electrophoretic mobility shift assays with wild type and mutant L2a elements. The data suggest that CDP/Cux bound to the L2a element is displaced by binding of SATB1 and the accompanying conformational change in the DNA lying between the primary binding sites of SATB1 and CDP/Cux. We suggest that displacement of CDP/Cux by SATB1 favors transcription of the CD8a gene, possibly by enhancing or altering its association with the nuclear matrix.

Animals↗
PubMed1997

Interior structure and seasonal mass redistribution of Mars from radio tracking of Mars Pathfinder.

Doppler and range measurements to the Mars Pathfinder lander made using its radio communications system have been combined with similar measurements from the Viking landers to estimate improved values of the precession of Mars' pole of rotation and the variation in Mars' rotation rate. The observed precession of -7576 +/- 35 milliarc seconds of angle per year implies a dense core and constrains possible models of interior composition. The estimated annual variation in rotation is in good agreement with a model of seasonal mass exchange of carbon dioxide between the atmosphere and ice caps.

Atmosphere↗
PubMed1998

Topography of the northern hemisphere of Mars from the Mars Orbiter Laser Altimeter.

The first 18 tracks of laser altimeter data across the northern hemisphere of Mars from the Mars Global Surveyor spacecraft show that the planet at latitudes north of 50 degrees is exceptionally flat; slopes and surface roughness increase toward the equator. The polar layered terrain appears to be a thick ice-rich formation with a non-equilibrium planform indicative of ablation near the periphery. Slope relations suggest that the northern Tharsis province was uplifted in the past. A profile across Ares Vallis channel suggests that the discharge through the channel was much greater than previously estimated. The martian atmosphere shows significant 1-micrometer atmospheric opacities, particularly in low-lying areas such as Valles Marineris.

Atmosphere↗
PubMed1997

Selection of multiple-antibiotic-resistant (mar) mutants of Escherichia coli by using the disinfectant pine oil: roles of the mar and acrAB loci.

Mutants of Escherichia coli selected for resistance to the disinfectant pine oil or to a household product containing pine oil also showed resistance to multiple antibiotics (tetracycline, ampicillin, chloramphenicol, and nalidixic acid) and overexpressed the marA gene. Likewise, antibiotic-selected Mar mutants, which also overexpress marA, were resistant to pine oil. Deletion of the mar or acrAB locus, the latter encoding a multidrug efflux pump positively regulated in part by MarA, increased the susceptibility of wild-type and mutant strains to pine oil.

Ampicillin↗
PubMed1998

Observations of the north polar region of Mars from the Mars orbiter laser altimeter.

Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H2O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 x 10(6) to 1.7 x 10(6) cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.

Carbon Dioxide↗
PubMed1998

The structure of the upper atmosphere of mars: In situ accelerometer measurements from mars global surveyor

The Mars Global Surveyor (MGS) z-axis accelerometer has obtained over 200 vertical structures of thermospheric density, temperature, and pressure, ranging from 110 to 170 kilometers, compared to only three previous such vertical structures. In November 1997, a regional dust storm in the Southern Hemisphere triggered an unexpectedly large thermospheric response at mid-northern latitudes, increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm. Throughout the MGS mission, thermospheric density bulges have been detected on opposite sides of the planet near 90 degreesE and 90 degreesW, in the vicinity of maximum terrain heights. This wave 2 pattern may be caused by topographically-forced planetary waves propagating up from the lower atmosphere.

Journal Article↗
PubMed1998

Early views of the martian surface from the Mars Orbiter Camera of Mars Global Surveyor.

High-resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms. Dunes, sandsheets, and drifts are prevalent and exhibit a range of morphology, composition (inferred from albedo), and age (as seen in occurrences of different dune orientations at the same location). Steep walls of topographic depressions such as canyons, valleys, and impact craters show the martian crust to be stratified at scales of a few tens of meters. The south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non-volatile components. Low resolution regional views of the planet provide synoptic observations of polar cap retreat, condensate clouds, and the lifecycle of local and regional dust storms.

Carbon Dioxide↗
PubMed1990

[The treatment of imported Plasmodium falciparum malaria with halofantrine. Apropos of 59 case reports (corrected and republished article orginally printed in Med Trop (Mars) 1990 Jan-Mar;50(1):113-7)].

59 cases of Plasmodium falciparum malaria fever occurring in non-immune Caucasian subjects having got a correct chemoprophylaxis by chloroquine were treated by halofantrine (HALFAN). They were given 1500 mg divided in 3 doses of 500 mg every 6 hours from D1 to D8. All them were back from a malarial highly endemic zone with chloroquine resistance. Analysis of the main biological and clinical efficiency parameters displayed very satisfactory results: disappearances of fever (mean 22 H) and parasitemia (mean 36 H) are short. After two months of monitoring, no malaria recrudescence was noted. With an efficacy of 10 p.c. associated to a noticeable clinical and biological tolerance Halofantrine is a first-class treatment of chloroquine resistant malaria fever.

Adolescent↗
PubMed1990

A novel monoclonal antibody, Mar 1, directed specifically against mononuclear phagocyte system cells in rats.

Three different monoclonal antibodies (mAb), designated Mar 1, Mar 2, and Mar 3, recognizing three distinct novel antigen molecules expressed preferentially in rat macrophages, were produced by the hybridoma technique. Binding of these mAb to isolated cells or fixed cells was detected by radioactive binding assay, immunohistochemical technique and flow cytometry. Mar 1 binds specifically to the cells constituting the mononuclear phagocyte system (MPS), but not to granulocytes nor endocytosis-positive cells from non-lymphoid tissues. Mar 2 and Mar 3 recognize both the former and the latter. The isotypes of Mar 1, Mar 2 and Mar 3 were defined as IgG1, IgG1 and IgG2b, respectively. These mAb were species specific, allo-non-specific and not cytotoxic for rat peritoneal macrophages. Immunoelectron microscopic observation demonstrated that Mar 1-3 antigens are located on both surface membrane and cytoplasmic membrane structures of peritoneal macrophages, particularly on the limiting membrane of phagocytic small vesicles and large phagosomes. Immunoprecipitation experiments demonstrated that the apparent molecular weights (MW) of the reactive antigens of Mar 1, Mar 2 and Mar 3 are 95,000, 100,000 and 55,000 and 27,000, respectively. These findings indicate that all of Mar 1-3 mAb have considerable value in the identification of rat phagocytes and that, of the three kinds of antigens detected with Mar 1-3, Mar 1 antigen is a specific marker for identification of the cells constituting the MPS and may offer the means to assess the functional capability and differentiation process of the macrophage populations.

Animals↗
PubMed1988

marA locus causes decreased expression of OmpF porin in multiple-antibiotic-resistant (Mar) mutants of Escherichia coli.

Mar (multiple antibiotic resistant) mutants of Escherichia coli express chromosomally mediated resistance to a variety of structurally unrelated hydrophilic and hydrophobic antibiotics. Insertion of transposon Tn5 into the marA locus at min 34.05 on the chromosome completely reverses the Mar phenotype (A. M. George and S. B. Levy, J. Bacteriol. 155:531-540, 1983). We found that among changes in the outer membrane of Mar mutants, porin OmpF was greatly reduced, although Mar mutants were more resistant than cells lacking only OmpF. Transduction of the marA region from a Mar strain, but not a wild-type strain, led to loss of OmpF. P1 transduction of marA::Tn5 into a Mar mutant partially restored OmpF levels. Therefore, OmpF reduction required a mutation in the marA region. Mar mutants of an ompF-lacZ operon fusion strain expressed 50 to 75% of the beta-galactosidase activity of the isogenic non-Mar parental strain, while Mar mutants of a protein fusion strain expressed less than 10% of the enzyme activity in the non-Mar strain. These changes were completely reversed by insertion of marA::Tn5. The responsiveness of OmpF-LacZ to osmolarity and temperature changes was similar in Mar and wild-type strains. Although some transcriptional control may have been present, OmpF reduction appeared to occur primarily by a posttranscriptional mechanism. The steady-state levels of ompF mRNA were twofold lower and the mRNA was five times less stable in the Mar mutant than in the wild-type strain. Expression of micF, which lowers ompF mRNA levels, was elevated in Mar strains, as revealed by a micF-lacZ fusion. Studies with strains deleted for the micF locus showed that the marA-dependent reduction of OmpF required an intact micF locus. Our findings suggest that the marA locus directly or indirectly increases micF expression, causing a posttranscriptional decrease in ompF mRNA and reduced amounts of OmpF.

Bacterial Outer Membrane Proteins↗
PubMed1986

Antigenic variation (mar mutations) in herpes simplex virus glycoprotein B can induce temperature-dependent alterations in gB processing and virus production.

Monoclonal antibody-resistant (mar) mutants altered in the antigenic structure of glycoprotein B (gB) of herpes simplex virus type 1, strain KOS-321, were selected by neutralization with each of six independently derived gB-specific monoclonal antibodies. Analysis of the reactivity patterns of these mar mutants with a panel of 16 virus-neutralizing monoclonal antibodies identified at least five nonoverlapping epitopes on this antigen, designated groups I through V. Multiple mar mutations were also introduced into the gB structural gene by recombination and sequential antibody selection to produce a set of mar mutants with double, triple, and quadruple epitope alterations. Group II (B2) and group III (B4) antibodies were used to select the corresponding mutants, mar B2.1 and mar B4.1, which in addition to carrying the mar phenotype were temperature sensitive (ts) for processing of the major partially glycosylated precursor of gB, pgB (Mr = 107,000), to mature gB (Mr = 126,000) and showed reduced levels of gB on the cell surface at high temperature (39 degrees C). These mutants were not, however, ts for production of infectious progeny. A recombinant virus, mar B2/4.1, carrying both of these alterations was ts for virus production and failed to produce and transport any detectable mature gB to the cell surface at 39 degrees C. Rather, pgB accumulated in the infected cell. Revertants of the ts phenotype, isolated from virus plaques at 39 degrees C, regained the B2 but not the B4 epitope and were phenotypically indistinguishable from the mar B4.1 parent. Finally, it was shown that group II (B5) and group III (B4) antibodies failed to immunoprecipitate pgB (39 degrees C) produced by ts gB mutants of herpes simplex virus type 1 which were not selected with monoclonal antibodies. Taken together, our findings indicate that (i) mar mutations can alter antigenic as well as other functional domains of gB, namely, the domain(s) involved in processing and infectivity, and (ii) group II and group III epitopes lie within an essential functional domain of gB which is a target for ts gB mutations.

Antibodies, Monoclonal↗
PubMed1995

Preferential cross-linking of matrix-attachment region (MAR) containing DNA fragments to the isolated nuclear matrix by ionizing radiation.

The sequences that anchor DNA, matrix-attachment regions (MARs), can be identified by their specific and preferential binding to the nuclear matrix. This microenvironment may be hypersensitive to the formation of ionizing radiation-induced DNA damage, including DNA-protein cross-links (DPC). To examine the induction of DPC at or near MARs, we developed an in vitro binding assay by using nuclear matrices isolated from murine erythroleukemia cells by high-salt extraction of DNase I-digested nuclei. The cross-linking of nuclear matrix protein to DNA fragments containing kappa-immunoglobulin (kappa-Ig) or an hsp 70 MAR was studied. Fragments of pBR322 of similar size to the MAR-containing fragments served as non-MAR controls. Two types of experiments were conducted: type A in which nuclei were irradiated and nuclear matrices were isolated and assayed for the binding of exogenous 32P-labeled DNA fragments, and type B in which mixtures of isolated nuclear matrices and [32P]DNAs were irradiated and assayed for binding. Poly(dAT) served as a competitor in the binding assays, because it eliminated nonspecific binding of DNA to the nuclear matrix and revealed the radiation-induced increase in tightly bound DNA. When nuclear matrices were isolated from irradiated nuclei (0-200 Gy) and incubated with the kappa-Ig MAR fragment in the absence of poly(dAT) (type A experiments), much nonspecific, non-dose-dependent binding was observed. With poly(dAT) in the incubation mixture, a dose-dependent decrease (p < 0.001) in the binding was revealed, indicating a radiation-induced loss of available binding sites, perhaps due to the cross-linking of endogenous sequences. The pBR322 fragment did not show a similar loss of binding sites. Irradiation of mixtures of isolated nuclear matrices and end-labeled fragments (type B experiments) allowed the study of radiation-induced cross-linking of exogenous fragments to the matrices. If poly(dAT) was present during irradiation, nonspecific binding was eliminated; however, no significant increase (p = 0.5) in the specific binding of the DNA to the nuclear matrix was observed. In contrast, if poly(dAT) was added after irradiation, in addition to the elimination of nonspecific binding, a radiation dose-dependent increase in binding was revealed for both the kappa-Ig MAR and the hsp MAR (p < 0.001), but not for either of the pBR322 fragments. The results indicate that the specific interaction of MARs with proteins of the nuclear matrix provides a radiation-sensitive substrate for the formation of DNA-protein cross-links.

Animals↗
PubMed1994

Transcription factor binding sites in the matrix attachment region (MAR) of the chicken alpha-globin gene.

Nuclear matrix is a nuclear protein-DNA superstructure believed to be the exclusive site of DNA replication, transcription, repair, and recombination. The attachment regions of chromatin loops to the nuclear matrix, called MARs, nest origins of replication, have transcriptional enhancer activity, and via their interaction with protein transcription factors may govern gene switch during development and tissue-specific gene expression. In this study the 967 bp MAR of the chicken alpha-globin gene is analyzed for the presence of hexanucleotides from a number (83 in total) of vertebrate protein transcription factors and core origins of replication. A total number of 760 hexanucleotides from factor sites or origins of replication were used for this search. We found that: (1) The occurrence of protein transcription factor binding sites overall on the MAR fragment as well as on the enhancer and promoter regions of other genes is only about 1.2-1.5 times higher than in random DNA, something consistent for all MAR and enhancer sequences examined. However, a high concentration (up to 2.7 times over random sequences) of hexanucleotide factor sites is observed on small stretches of the alpha-globin gene MAR. (2) Some regulatory protein binding sites are underrepresented whereas others are overrepresented, giving to an MAR a particular transcription factor flavor. (3) The DNA curvature map of the MAR sequence and the potential sites of positioned nucleosomes suggest the sites where a competition between core histone octamers and protein transcription factors for DNA might be found. This approach might provide a novel technique to diagnose for the regulatory or nonregulatory function of a stretch of DNA. Furthermore, MARs are proposed to constitute important regulatory elements of genes in addition to enhancers, promoters, silencers, locus control regions, and origins of replication. Additional parameters such as interaction of a transcription factor with other transcription factors fixed at vicinal sites, DNA methylation, intrinsic DNA curvature torsional strain, and nucleosome positioning might also determine the high-affinity binding of a transcription factor to its functional sites and its exclusion from or low affinity binding to other nonregulatory regions.

Animals↗
PubMed1995

Chromatin domains and prediction of MAR sequences.

Polynuceosomes are constrained into loops or domains and are insulated from the effects of chromatin structure and torsional strain from flanking domains by the cross-complexation of matrix-attached regions (MARs) and matrix proteins. MARs or SARs have an average size of 500 bp, are spaced about every 30 kb, and are control elements maintaining independent realms of gene activity. A fraction of MARs may cohabit with core origin replication (ORIs) and another fraction might cohabit with transcriptional enhancers. DNA replication, transcription, repair, splicing, and recombination seem to take place on the nuclear matrix. Classical AT-rich MARs have been proposed to anchor the core enhancers and core origins complexed with low abundancy transcription factors to the nuclear matrix via the cooperative binding to MARs of abundant classical matrix proteins (topoisomerase II, histone H1, lamins, SP120, ARBP, SATB1); this creates a unique nuclear microenvironment rich in regulatory proteins able to sustain transcription, replication, repair, and recombination. Theoretical searches and experimental data strongly support a model of activation of MARs and ORIs by transcription factors. A set of 21 characteristics are deduced or proposed for MAR/ORI sequences including their enrichment in inverted repeats, AT tracts, DNA unwinding elements, replication initiator protein sites, homooligonucleotide repeats (i.e., AAA, TTT, CCC), curved DNA, DNase I-hypersensitive sites, nucleosome-free stretches, polypurine stretches, and motifs with a potential for left-handed and triplex structures. We are establishing Banks of ORI and MAR sequences and have undertaken a large project of sequencing a large number of MARs in an effort to determine classes of DNA sequences in these regulatory elements and to understand their role at the origins of replication and transcriptional enhancers.

Animals↗