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S Silver

Publications and source records attributed to S Silver.

At least 91 records · Page 5Linked to original sources
PubMed1990

Nucleotide sequence and expression of a plasmid-encoded chromate resistance determinant from Alcaligenes eutrophus.

The nucleotide sequence of the 2.6-kilobase pair (kb) EcoRI fragment encoding chromate resistance (Chrr) on plasmid pMOL28 in Alcaligenes eutrophus was determined. Three open reading frames were assigned to three polypeptides which were expressed from this determinant in Escherichia coli under the control of a phage T7 transcription promoter. When the roles of the polypeptides and open reading frames were analyzed with deletion derivatives of the 2.6-kilobase fragment, the membrane-bound ChrA (401 amino acids) and ChrB (196 amino acids) polypeptides were essential for inducible chromate resistance and reduced accumulation of chromate, while the third open reading frame was not needed.

Alcaligenes↗
PubMed1990

Human monoclonal antibody that recognizes the V3 region of human immunodeficiency virus gp120 and neutralizes the human T-lymphotropic virus type IIIMN strain.

We describe a human IgG1 monoclonal antibody (N701.9b) derived by Epstein-Barr virus transformation of B cells from a human immunodeficiency virus-seropositive asymptomatic donor. This antibody was shown to recognize the principal neutralizing domain contained within the V3 region of gp120 of the MN strain of human immunodeficiency virus and MN-like strains, as determined by binding to the PB-1 fragment of MN gp120 and to synthetic peptides corresponding to the V3 region of MN and related virus strains. The epitope identified by monoclonal antibody N701.9b was mapped to a segment of V3 containing at least 7 amino acids (amino acids 316-322), which is located in the "tip" and "right" side of the V3 loop of the MN strain. Furthermore, this antibody manifested potent type-specific fusion-inhibitory activity against the MN strain but not against the IIIB or RF virus strains. This antibody also neutralized four virus isolates that had MN-like V3 region sequences and failed to neutralize three other strains containing unrelated V3 region sequences. Our findings confirm that the V3 region stimulates type-specific neutralizing antibody during natural human immunodeficiency virus infection in humans. The potential clinical use of this antibody is discussed.

Amino Acid Sequence↗
PubMed1990

Chromium reduction in Pseudomonas putida.

Reduction of hexavalent chromium (chromate) to less-toxic trivalent chromium was studied by using cell suspensions and cell-free supernatant fluids from Pseudomonas putida PRS2000. Chromate reductase activity was associated with soluble protein and not with the membrane fraction. The crude enzyme activity was heat labile and showed a Km of 40 microM CrO4(2-). Neither sulfate nor nitrate affected chromate reduction either in vitro or with intact cells.

Chromates↗
PubMed1990

Cloning, nucleotide sequence, and expression of the chromate resistance determinant of Pseudomonas aeruginosa plasmid pUM505.

The chromate resistance determinant of Pseudomonas aeruginosa plasmid pUM505 was cloned into broad-host-range vector pSUP104. The hybrid plasmid containing an 11.1-kilobase insert conferred chromate resistance and reduced uptake of chromate in P. aeruginosa PAO1. Resistance to chromate was not expressed in Escherichia coli. Contiguous 1.6- and 6.3-kilobase HindIII fragments from this plasmid hybridized to pUM505 but not to P. aeruginosa chromosomal DNA and only weakly to chromate resistance plasmids pLHB1 and pMG6. Further subcloning produced a plasmid with an insert of 2,145 base pairs, which was sequenced. Analysis of deletions revealed that a single open reading frame was sufficient to determine chromate resistance. This open reading frame encodes a highly hydrophobic polypeptide, ChrA, of 416 amino acid residues that appeared to be expressed in E. coli under control of the T7 promoter. No significant homology was found between ChrA and proteins in the amino acid sequence libraries, but 29% amino acid identity was found with the ChrA amino acid sequence for another chromate resistance determinant sequenced in this laboratory from an Alcaligenes eutrophus plasmid (A. Nies, D. Nies, and S. Silver, submitted for publication).

Amino Acid Sequence↗
PubMed1990

Constitutive synthesis of a transport function encoded by the Thiobacillus ferrooxidans merC gene cloned in Escherichia coli.

Mercuric reductase activity determined by the Thiobacillus ferrooxidans merA gene (cloned and expressed constitutively in Escherichia coli) was measured by volatilization of 203Hg2+. (The absence of a merR regulatory gene in the cloned Thiobacillus mer determinant provides a basis for the constitutive synthesis of this system.) In the absence of the Thiobacillus merC transport gene, the mercury volatilization activity was cryptic and was not seen with whole cells but only with sonication-disrupted cells. The Thiobacillus merC transport function was compared with transport via the merT-merP system of plasmid pDU1358. Both systems, cloned and expressed in E. coli, governed enhanced uptake of 203Hg2+ in a temperature- and concentration-dependent fashion. Uptake via MerT-MerP was greater and conferred greater hypersensitivity to Hg2+ than did uptake with MerC. Mercury uptake was inhibited by N-ethylmaleimide but not by EDTA. Ag+ salts inhibited mercury uptake by the MerT-MerP system but did not inhibit uptake via MerC. Radioactive mercury accumulated by the MerT-MerP and by the MerC systems was exchangeable with nonradioactive Hg2+.

Biological Transport↗
PubMed1989

HIV infection: continuing education for health professionals.

In future years, it will become common for individuals in essentially every health profession to be involved in the care of a person infected with the Human Immunodeficiency Virus (HIV). Educators face the task of preparing future health providers as well as ensuring career entry knowledge to practicing practitioners. This paper discusses education programs concerning HIV disease in relation to methods of presentation, program content, and presentation considerations. Various resources available to those planning HIV education programs also are described.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Down regulation of the mercury resistance operon by the most promoter-distal gene merD.

The effect of the merD gene on the expression of the mer operon was determined from the rates of accumulation of merA-lacZ fusion protein in the presence and absence of an active merD gene in trans. In the presence of the merD gene, beta-galactosidase activity was 2- to 4-fold lower. The merD gene was cloned in a T7 promoter expression vector and the MerD protein product was visualized by autoradiography.

Amino Acid Sequence↗
PubMed1989

Bacterial resistance ATPases: primary pumps for exporting toxic cations and anions.

Bacterial plasmid resistance systems that maintain low intracellular levels of toxic heavy metals by pumping the substrates out as rapidly as they accumulate sometimes work at the biochemical level as efflux ATPases. The two systems responsible for arsenic and cadmium resistance have recently been sequenced. Comparison of the deduced amino acid sequences with those of better characterized ATPases has revealed certain structural and sequence similarities.

Adenosine Triphosphatases↗
PubMed1989

Cadmium resistance from Staphylococcus aureus plasmid pI258 cadA gene results from a cadmium-efflux ATPase.

Cadmium resistance specified by the cadA determinant of Staphylococcus aureus plasmid pI258 results from the functioning of a cadmium-efflux system. In the nucleotide sequence of the DNA fragment containing the cadA determinant, two open reading frames were identified. The larger one, corresponding to a predicted polypeptide of 727 amino acid residues, is necessary and sufficient for expression of cadmium resistance. Comparison of the CadA amino acid sequence with known protein sequences suggested that CadA is a member of the E1E2 cation-translocating ATPases, similar to the K+-uptake ATPases of Gram-positive and Gram-negative bacteria. The sequence homology is lower but significant with other E1E2-type ATPases, including the H+-efflux ATPases of eukaryotic microbes and the Ca2+- and Na+/K+-ATPases of animals. A frame-shift mutation in the middle of the gene destroys the Cd2+-resistance phenotype. A detailed model for the putative CadA ATPase based on homologies to other E1E2 ATPases is presented and discussed.

Adenosine Triphosphatases↗
PubMed1989

Expression and nucleotide sequence of a plasmid-determined divalent cation efflux system from Alcaligenes eutrophus.

Resistance to cobalt, zinc, and cadmium specified by the czc determinant on plasmid pMOL30 in Alcaligenes eutrophus results from a cation efflux system. Five membrane-bound polypeptides that were expressed in Escherichia coli from this determinant under the control of a phage T7 promoter were assigned to four open reading frames identified in the nucleotide sequence of the 6881-base-pair fragment containing the czc putative operon. The contributions of the polypeptides to the cation efflux system were analyzed with deletion derivatives of the 6.9-kilobase fragment, constructed, and expressed in E. coli under the control of the phage T7 promoter and in A. eutrophus under the control of the lac promoter.

Alcaligenes↗
PubMed1989

Cell-free mercury volatilization activity from three marine caulobacter strains.

Three mercury-resistant marine Caulobacter strains showed an inducible mercury volatilization activity. Cell-free mercury volatilization (mercuric reductase) from these three marine Caulobacter strains was characterized and compared with enzyme activities determined by plasmids of Escherichia coli and Staphylococcus aureus. The temperature sensitivity of the Caulobacter mercuric reductase was greater than that of mercuric reductase from other gram-negative sources. Cell-free enzyme activity required NADH or NADPH, with NADPH functioning much better at lower concentrations than NADH. The Km for the Caulobacter enzyme was 4 microM Hg2+. Ag+ was a competitive inhibitor of Caulobacter mercuric reductase (Ki = 0.2 microM Ag+), as with previously studied enzymes. Arsenite was a noncompetitive inhibitor of the Caulobacter enzyme with a Ki of 75 microM AsO2-.

Bacteria↗
PubMed1989

Nucleotide sequence of a chromosomal mercury resistance determinant from a Bacillus sp. with broad-spectrum mercury resistance.

A 13.5-kilobase HindIII fragment, bearing an intact mercury resistance (mer) operon, was isolated from chromosomal DNA of broad-spectrum mercury-resistant Bacillus sp. strain RC607 by using as a probe a clone containing the mercury reductase (merA) gene. The new clone, pYW33, expressed broad-spectrum mercury resistance both in Escherichia coli and in Bacillus subtilis, but only in B. subtilis was the mercuric reductase activity inducible. Sequencing of a 1.8-kilobase mercury hypersensitivity-producing fragment revealed four open reading frames (ORFs). ORF1 may code for a regulatory protein (MerR). ORF2 and ORF4 were associated with cellular transport function and the hypersensitivity phenotype. DNA fragments encompassing the merA and the merB genes were sequenced. The predicted Bacillus sp. strain RC607 MerA (mercuric reductase) and MerB (organomercurial lyase) were similar to those predicted from Staphylococcus aureus plasmid pI258 (67 and 73% amino acid identities, respectively); however, only 40% of the amino acid residues of RC607 MerA were identical to those of the mercuric reductase from gram-negative bacteria. A 69-kilodalton polypeptide was isolated and identified as the merA gene product by examination of its amino-terminal sequence.

Amino Acid Sequence↗
PubMed1989

Mercury operon regulation by the merR gene of the organomercurial resistance system of plasmid pDU1358.

The structural basis for induction of the mercury resistance operon with inorganic mercury and with the organomercurial compound phenylmercuric acetate was addressed by DNA sequencing analysis and by lac fusion transcription experiments regulated by merR in trans from broad-spectrum-resistance plasmid pDU1358 (Hg2+ and phenylmercury responding). The lac fusion results were compared with those from a narrow-spectrum-resistance (Hg2+ responding but not phenylmercuric responding) operon and the pDU1358 merR deleted at the 3' end. The nucleotide sequence of the beginning region of the broad-spectrum mer operon of plasmid pDU1358 was determined, including that of the merR gene, the operator-promoter region, the merT and merP genes, and the first 60% of the merA gene. Comparison of this sequence with DNA sequences of narrow-spectrum mer operons from transposon Tn501 and plasmid R100 showed that a major difference occurred in the 3' 29 base pairs of the merR gene, resulting in unrelated C-terminal 10 amino acids. A hybrid mer operon consisting of the merR gene from pDU1358, a hybrid merA gene (determining mercuric reductase enzyme), and lacking the merB gene (determining phenylmercury lyase activity) was inducible by both phenylmercury and inorganic Hg2+. This shows that organomercurial lyase is not needed for induction by organomercurial compounds. A mutant form of pDU1358 merR missing the C-terminal 17 amino acids responded to inorganic Hg2+ but not to phenylmercury. Thus, the C-terminal region of the MerR protein of the pDU1358 mer operon is involved in the recognition of phenylmercury.

Amino Acid Sequence↗
PubMed1989

Cloning and expression of plasmid genes encoding resistances to chromate and cobalt in Alcaligenes eutrophus.

Resistances to chromate and cobalt were cloned on a 30-kilobase-pair (kb) DNA region from the large Alcaligenes eutrophus plasmid pMOL28 into the broad-host-range mobilizable cosmid vector pVK102. A restriction nuclease map of the 30-kb region was generated. The resistances expressed from the hybrid plasmids after transfer back into A. eutrophus were inducible and conferred the same degree of resistance as the parent plasmid pMOL28. Resistances were expressed in metal-sensitive Alcaligenes strains and related bacteria but not in Escherichia coli. Resistance to chromate was further localized on a 2.6-kb EcoRI fragment, and resistance to cobalt was localized on an adjoining 8.5-kb PstI-EcoRI fragment. When the 2.6-kb EcoRI fragment was expressed in E. coli under the control of a bacteriophage T7 promoter, three polypeptides with molecular masses of 31,500, 21,000, and 14,500 daltons were visible on autoradiograms. The 31,500- and 21,000-dalton polypeptides were membrane bound; the 14,500-dalton polypeptide was soluble.

Alcaligenes↗
PubMed1989

Acoustic trauma-induced Meniere's syndrome.

Eight male patients suffering from Menière's syndrome are presented. All patients sustained sudden or prolonged exposure to severe noise levels and suffer from acoustic trauma. The incidence of Menière's syndrome in our group of patients is significantly higher than in series reported in the normal population. Our presentation supports the implication of acoustic trauma as a possible cause of Menière's syndrome.

Adult↗