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T J Foster

Publications and source records attributed to T J Foster.

At least 109 records · Page 6Linked to original sources
PubMed1983

Tn5 insertion mutations in the mercuric ion resistance genes derived from plasmid R100.

The mercuric resistance (mer) genes of plasmid R100 were cloned into plasmid pBR322. A series of transposon Tn5 insertion mutations in the mer genes were isolated and mapped. The mutants were characterized phenotypically by their sensitivity to Hg2+ and by binding and volatilization of 203Hg2+. Dominance and complementation tests were also performed. Mutations affecting the previously described mer genes merR (regulation), merT (transport), and merA (reductase) were characterized. Evidence was obtained for two new mer genes, which have been called merC and merD. A restriction enzyme map of the mer region was drawn with the gene order merRTCAD. Transcriptional merR-lac and merA-lac fusions were generated by insertion of phage Mu d amp lac into plasmid R100-1. These were used to study regulation of mer gene expression. The merR gene product appears to regulate negatively its own expression as well as acting as both a negative and a positive regulator of the merTCA genes.

DNA Transposable Elements↗
PubMed1982

Nonenzymatic chloramphenicol resistance determinants specified by plasmids R26 and R55-1 in Escherichia coli K-12 do not confer high-level resistance to fluorinated analogs.

Plasmids R26 (Inc P) and R55-1 (Inc C) specify inducible nonenzymatic resistance to chloramphenicol. Escherichia coli K-12 strains harboring these plasmids encoded low-level resistance to thiamphenicol analogs Sch 25298 and Sch 25393 but failed to specify resistance to the fluorinated chloramphenicol analog Sch 24893. The analogs were efficient inducers of high-level chloramphenicol resistance.

Chloramphenicol↗
PubMed1981

Genetic organization of transposon Tn10.

Transposon Tn10 is 9300 bp in length, with 1400 bp inverted repeats at its ends. The inverted repeats are structurally intact IS-like sequences (Ross et al., 1979). Analysis of deletion mutants and structural variants of Tn10, reported below, shows that the two IS10 segments contain all of the Tn10-encoded genetic determinants, both sites and functions, that are required for transposition. Furthermore, the two repeats (IS10-Right and IS10-Left) are not functionally equivalent: IS10-Right is fully functional and is capable by itself of promoting normal levels of Tn10 transposition; IS10-Left functions only poorly by itself, promoting transposition at a very low level when IS10-Right is inactivated. Complementation analysis shows that IS10-Right encodes at least one function, required for Tn10 transposition, which can act in trans and which works at the ends of the element. Also, all of the sites specifically required for normal Tn10 transposition have been localized to the outermost 70 bp at each end of the element; there is no evidence that specific sites internal to the element play an essential role. Finally, Tn10 modulates its own transposition in such a way that transposition-defective point mutants, unlike deletion mutants, are not complemented by functions provided in trans; and wild-type Tn10, unlike deletion mutants, is not affected by functions provided in trans from a "high hopper" Tn10 element.

Base Sequence↗
PubMed1981

Three Tn10-associated excision events: relationship to transposition and role of direct and inverted repeats.

We describe three related DNA alterations associated with transposon Tn10: precise excision of Tn10, nearly precise excision of Tn10 and precise excision of the nearly precise excision remnant. DNA sequence analysis shows that each of these alterations results in excision of all or part of the Tn10 element, and each involves specific repeat sequences at or near the ends of the element. Furthermore, all three events are structurally analogous: in each case, excision occurs between two short direct-repeat sequences, with resulting deletion of all intervening material plus one copy of the direct repeat; and in all three cases, the direct repeats involved occur at either end of an inverted repeat. Analysis of mutant Tn10 elements and characterization of bacterial host mutations suggest that all three types of excision events occur by pathways that are fundamentally distinct from the pathway(s) for Tn10-promoted transposition and other DNA rearrangements (deletions and inversions) actively promoted by the element. In addition, precise excision and nearly precise excision appear to occur by very closely related or identical pathways; and several lines of evidence suggest that the 1400 bp inverted repeats at the ends of Tn10 may play a structural role in both of these events. The third excision event appears to occur by yet another pathway.

Base Sequence↗
PubMed1981

Plasmids in epidermolytic strains of Staphylococcus aureus.

Thirty-four epidermolytic toxin-producing strains of Staphylococcus aureus obtained from a variety of sources were screened for the presence of plasmid DNA. All serotype ii toxin producers harboured a large 42 kilobase pairs (kb) plasmid. Elimination of these plasmids resulted in the simultaneous loss of a bacteriocin determinant (Bac+) and type ii toxin production (Toxii+). Some strains producing serotype i toxin (Toxi+) contained similar 42 kb plasmids. Elimination of these plasmids resulted in the loss of only bacteriocin production. Strains producing both toxin serotypes readily lost Toxii+ and Bac+, which were carried on the same plasmid, but Toxi+ could not be eliminated. Thus Toxi+ was probably chromosomally determined, while Toxii+ was a plasmid-encoded marker. In some strains cadmium resistance was also linked to the 42 kb plasmid. The 42 kb plasmids from seven strains with different phenotypes were analysed with restriction endonucleases EcoRI and HindIII. The plasmids shared 19 of 22 HindIII fragments indicating that they are closely related to each other.

Bacterial Toxins↗
PubMed1981

Chloramphenicol resistance that does not involve chloramphenicol acetyltransferase encoded by plasmids from gram-negative bacteria.

Chloramphenicol resistance-specifying plasmids from incompatibility groups P-1 and C did not encode chloramphenicol acetyltransferase (CAT). Expression of resistance was inducible by subinhibitory concentrations of the drug. The mechanism of resistance was thought to be a cytoplasmic membrane-located barrier to the permeability of the drug into the cell. No evidence for the inactivation of the drug was obtained. In vitro polypeptide synthesis directed by ribosomes isolated from resistant and sensitive cells was equally sensitive to inhibition by chloramphenicol suggesting that a ribosomal mechanism was not involved. Spheroplasts expressed the same level of resistance as whole cells. Strains specifying intracellular CAT did not degrade chloramphenicol in the culture medium if they also carried a chloramphenicol resistance plasmid not specifying CAT.

Acetyltransferases↗
PubMed1979

Transposon 10 promoted deletions and inversions in the transfer genes of R100-1.

Spontaneous tetracycline-sensitive, transfer-deficient mutants of R100-1 were selected and analysed by genetic complementation tests and with the restriction endonuclease EcoR1. While some of the Tets Tra- mutants were caused by a single deletion event which removed the Tetr genes and extended into the neighbouring transfer genes, other mutants were the result of the deletion of the Tetr genes within Tn10 which was accompanied by an inversion of adjacent DNA sequences. A clustering of deletion and inversion endpoints occurred in the traA gene. Some of the transfer genes of R100-1 were assigned to EcoR1 fragments.

Chromosome Deletion↗
PubMed1979

Transposon A-generated mutations in the mercuric resistance genes of plasmid R100-1.

A series of 23 transposon 801(Tn801)-induced mutations of plasmid R100-1 from mercuric salts resistance to sensitivity was studied. Although Tn801 transposed frequently into the mer region of the plasmid, fine structural analysis showed that the site of insertion within mer varied. About one-half of the Tn801 insertion events also caused a deletion of greater than 1 megadalton. Genetic and restriction endonuclease EcoRI and BamHI analysis of the mutant plasmid deoxyribonucleic acid elucidated the organization of the mer operon and suggested the existence of a trans-acting regulatory factor governing resistance to mercuric salts. Tn801 insertions leading to mercuric sensitivity occurred in the restriction endonuclease fragments EcoRI-H and EcoRI-I. Regulatory mutations leading to a 50-fold-reduced synthesis of mercuric reductase enzyme occurred in two complementation classes thought to represent the gene for a trans-acting inducer molecule and a cis-acting operator-promoter sequence. Mutations leading to total loss of the enzyme mercuric reductase occurred on both the EcoRI-H and EcoRI-I fragments, showing that the structural gene for this enzyme (merA) bridges the EcoRI cleavage site separating the segments. Hypersensitivity to mercuric salts resulted when Tn801 insertion occurred in the reductase gene in the operatordistal portion of the operon. Hypersensitive cells inducibly bound three to five times more Hg2+ at low concentrations than did sensitive (plasmidless) cells. This finding led to the proposal that another gene (merT) controls uptake of Hg2+ by the cells. Transcription of the operon was deduced to start in the EcoRI-H fragment and to move into the EcoRI-I fragment of the plasmid genome.

DNA Transposable Elements↗
PubMed1979

Deletions in the r-determinant mer region of plasmid R100-1 selected for loss of mercury hypersensitivy.

A mutant of plasmid R100-1, which conferred cellular hypersensitivity to Hg2+ because of the insertion of Tn801 (TnA) into the gene determining synthesis of mercuric reductase enzyme, allowed further mutational events to be selected which resulted in either reversion to Hg2+ resistance (characteristic plasmid R100-1) or sensitivity at a level characteristic of plasmidless strains. Restriction endonuclease EcoRI and BamHI analysis showed that reversion to resistance resulted from loss of TnA from the R100-mer:Tn801 plasmid, whereas the change from hypersensitivity to sensitivity to Hg2+ usually resulted from deletion of part or all of Tn801 plus plasmid deoxyribonucleic acid sequences corresponding to the operator-proximal end of the mer operon.

DNA Transposable Elements↗
PubMed1977

Genetic analysis of mutations in the transfer genes of pDU202 tra::Tn10 plasmids, caused by the excision of Tn10.

Transfer-deficient derivatives of pDU202 (a Tcs deletion mutant of R100-1) caused by the insertion of Tn10 into the R factor's transfer genes have been described previously. Tetracyline-sensitive mutants of four of these were selected. In the majority of cases the Tcs mutation was caused by a deletion of the Tcr genes which was often accompanied either by a deletion of some of the flanking transfer genes or by a secondary mutation which was probably an inversion. A number of preferred end points for the deletions and inversions occur in the transfer operon of pDU202. Analysis of the mutants by complementation tests with Flac tra elements confirmed that the order of genes in the promoter distal part of the tra region of pDU202 is traKBCFHGSD and traI.

Escherichia coli↗
PubMed1977

Insertion of the tetracycline resistance translocation unit Tn10 in the lac operon of Escherichia coli K12.

The majority of TN10 insertions in the lacZ gene of Escherichia coli occurred in a small region of the promoter distal part of the gene. The resulting mutations were polar on lacY and reverted to Lac+ at a frequency of 10(-8). None of the revertants were Tcr. Furthermore Lac+ Tcr revertants could not be selected directly. Relief of polarity revertants of the lacZ::Tn10 mutants were formed at a frequency of 10(-5) - 10(-4). Most resulted from a deletion event internal to the transposon which removed the Tcr genes and the putative transcription terminator. It is postulated that a fragment of Tn10 remains at the original insertion point to cause a revertible Lac- mutation.

Chromosome Mapping↗
PubMed1976

R factor-mediated tetracycline resistance in Escherichia coli K12. Dominance of some tetracycline sensitive mutants and relief of dominance by deletion.

Strains of Escherichia coli K12 heterozygous for the R100-1 tetracycline resistance region were constructed. They carried the wild-type Tetr genes in the chromosome and single site Tets mutations on plasmids. Some heterozygotes could not express tetracycline resistance fully after induction. The mutant tet allele was thus partially dominant. When heterozygotes carrying the dominant tet mutant were plated on agar containing 20 mg/ml tetracycline, mutants which grew normally occurred at a frequency of 1-4 X 10(-4). Analysis of these dominance relief mutants showed that in 53/56 isolates the dominant tet allele was lost forming either Tra+ or Tra- deletion mutants of the plasmid. The mutation frequency was not affected either by the host chromosomal recA mutation or by the temperature of growth of the culture.

Chromosome Deletion↗
PubMed1976

Genetic analysis of deletions of R100-1 that are both transfer-deficient and tetracycline-sensitive.

The extent of the deletions of five Tets Tra- mutants of R100-1 was determined by complementation experiments with wild-type and tra mutants of Flac. The presence or absence of the origin of transfer on the mutants was also investigated. Using the results, a tentative map of this region of the R factor was drawn: it was essentially similar to the analogous region of the E. coli K12 F factor, except that tet was located between traJ and traA. Some of the deletions had removed the promoter for the transfer operon. This allowed detection of the transcription of traC and distal genes from a weak, traJ-independent promoter. This is probably the Is2 promoter, since R100-1 carries and Is2 insertion sequence located immediately to the left of traC in the correct orientation. Since neither the transfer operon promoter nor the Is2 promoter seemed to be required for transcription of traI, it was concluded that, unlike the F factor, this was located in a separate operon.

Chromosome Mapping↗
PubMed1975

Tetracycline-sensitive mutants of the F-like R factors R100 and R100-1.

The majority of tetracycline-sensitive (Tets) mutants of R100 and R100-1 are multisite (deletion) mutants. About 50% of these are also transfer-deficient, indicating that the Tetr locus is closely linked to the transfer genes. Tet(s) mutants with single-site lesions are also described.

Chromosome Deletion↗
PubMed1975

R factor tetracycline and chloramphenicol resistance in Escherichia coli K12 cmlB mutants.

The isolation of Escherichia coli chromosomal mutants that increased the level of resistance of a partially tetracycline-sensitive mutant of RI00-I is described. Plasmid-less derivatives of these moderately resistant mutants were phenotypically similar to the cmlB mutants described by Reeve (1966, 1968), and also mapped in the same region. The level of intrinsic resistance to both chloramphenicol and tetracycline was increased about twofold. Also, the levels of R factor-determined resistance to these drugs were increased by this host mutation and tetracycline resistance was expressed constitutively. A cmlB accumulated tetracycline at a threefold lower rate than the wild-type strain, and it is proposed that the mutants have an altered permeability to the drugs and that this acts synergistically with the products of the R factor chloramphenicol and tetracycline resistance genes.

Acetyltransferases↗