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S Silver

Publications and source records attributed to S Silver.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1988

Promoters and transcription of the plasmid-mediated citrate-utilization system in Escherichia coli.

The nucleotide sequence of an 878-bp BamHI-BglII restriction endonuclease fragment from citrate utilization transposon Tn3411 was determined, and was compared with that from plasmid pMS185 [Sasatsu et al., J. Bacteriol. 164 (1985) 983-993]. A long open reading frame for a 379-amino acid (aa) polypeptide (citB) was found 5' to the citA gene (431-aa membrane protein) in Tn3411 as well as in pMS185. Promoter regions were identified by RNA polymerase filter-binding assays, S1 nuclease mapping and cit-lac fusion experiments. The results indicated that two genes (citA and citB) have separate promoters, and the location of the promoter for the citB gene in the Tn3411 nucleotide sequence was different from that in pMS185. The regulation of transcription of the two genes (citA and citB) was characterized by the use of cit-lacZ fusions. The level of the citB promoter activity was about five-fold higher than that of the citA gene promoter, and transcription from both was not induced by citrate. Synthesis of the mRNA for the citB gene (especially with the wild-type Cit+ determinant) was suppressed by citrate, accompanying growth suppression of Escherichia coli. The citB gene expressed in E. coli minicells produced a membrane-associated 37.5-kDa polypeptide.

Amino Acid Sequence↗
PubMed1988

The role of operator position in SV40 T-antigen-mediated repression.

We have manipulated positional relationships between the SV40 early operator and promoter to study the repression of transcription by T antigen. Single or multiple insertions of T-antigen-binding region I resulted in only weak repression even when the operator was placed immediately adjacent to known promoter elements. The low levels of repression appear to reflect the intrinsic strength of the T-antigen-operator interaction.

Antigens, Polyomavirus Transforming↗
PubMed1988

Addition of growth hormone secretion signal to basic fibroblast growth factor results in cell transformation and secretion of aberrant forms of the protein.

Basic fibroblast growth factor (bFGF) is a potent mitogen for a wide variety of cell types. Unlike most growth factors, the primary translation product for bFGF appears to lack a secretory signal peptide. To explore the normal mode of bFGF release, as well as to investigate the growth factor's oncogenic potential, expression vectors were created for a bFGF cDNA and for a chimeric molecule in which the bFGF coding sequence was linked to the human growth hormone signal peptide sequence. Transfection of NIH3T3 cells with the bFGF cDNA vectors caused the synthesis of high levels of biologically active, cell-associated bFGF, but no evidence of transformation was detected. In contrast, the chimeric bFGF-signal peptide expression vector induced foci of transformation at a very high frequency. The transformed cells grew in soft agar and were tumorigenic in nude mice. The majority of the immunoreactive bFGF species made by the transformed cells was found in the conditioned medium and appeared to be posttranslationally modified, indicating that the chimeric bFGF-signal peptide molecule was processed through the secretory pathway. The secreted bFGF exhibited little mitogenic activity, suggesting that interaction of bFGF with its receptor likely occurs while the fusion protein is being processed along the secretory pathway.

Animals↗
PubMed1987

Cloning and DNA sequence of the mercuric- and organomercurial-resistance determinants of plasmid pDU1358.

The broad-spectrum mercurial-resistance plasmid pDU1358 was analyzed by cloning the resistance determinants and preparing a physical and genetic map of a 45-kilobase (kb) region of the plasmid that contains two separate mercurial-resistance operons that mapped about 20 kb apart. One encoded narrow-spectrum mercurial resistance to Hg2+ and a few organomercurials; the other specified broad-spectrum resistance to phenylmercury and additional organomercurials. Each determinant governed mercurial transport functions. Southern DNA X DNA hybridization experiments using gene-specific probes from the plasmid R100 mer operon indicated close homology with the R100 determinant. The 2153 base pairs of the promoter-distal part of the broad-spectrum Hg2+-resistance operon of pDU1358 were sequenced. This region included the 3'-terminal part of the merA gene, merD, unidentified reading frame URF1, and a part of URF2 homologous to previously sequenced determinants of plasmid R100. Between the merA and merD genes, an open reading frame encoding a 212 amino acid polypeptide was identified as the merB gene that determines the enzyme organomercurial lyase that cleaves the C--Hg bond of phenylmercury.

Amino Acid Sequence↗
PubMed1987

Nucleotide sequence and expression of the mercurial-resistance operon from Staphylococcus aureus plasmid pI258.

The mercurial-resistance determinant from Staphylococcus aureus plasmid pI258 is located on a 6.4-kilobase-pair Bgl II fragment. The determinant was cloned into both Bacillus subtilis and Escherichia coli. Mercury resistance was found only in B. subtilis. The 6404-base-pair DNA sequence of the Bgl II fragment was determined. The mer DNA sequence includes seven open reading frames, two of which have been identified by homology with the merA (mercuric reductase) and merB (organomercurial lyase) genes from the mercurial-resistance determinants of Gram-negative bacteria. Whereas 40% of the amino acid residues overall were identical between the pI258 merA polypeptide product and mercuric reductases from Gram-negative bacteria, the percentage identity in the active-site positions and those thought to be involved in NADPH and FAD contacts was above 90%. The 216 amino acid organomercurial lyase sequence was 39% identical with that from a Serratia plasmid, with higher conservation in the middle of the sequences and lower homologies at the amino and carboxyl termini. The remaining five open reading frames in the pI258 mer sequence have no significant homologies with the genes from previously sequenced Gram-negative mer operons.

Bacillus subtilis↗