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P T Barth

Publications and source records attributed to P T Barth.

34 records · Page 2Linked to original sources
PubMed1978

Copy numbers of coexisting plasmids in Escherichia coli K-12.

A strain of Escherichia coli K-12 carrying eight compatible and distinguishable plasmids was constructed. The amounts of plasmid DNA (measured as supercoiled molecules) per chromosome in this strain was about equal to the sum of the plasmid DNAs, extracted under controlled conditions, from strains each carrying one of the eight plasmids. Analysis of these DNA preparations showed that each plasmid in the multiplasmid strain was present in the same proportion per chromosome as in the single-plasmid strains. Also the level of phenotypic expression of each plasmid in the multiplasmid strain was the same as in the single-plasmid strains. Each plasmid, therefore, appears to control its own copy number irrespective of the presence of other compatible plasmids.

Conjugation, Genetic↗
PubMed1977

Two naturally occurring transposons indistinguishable from Tn7.

Two plasmids from different sources, determining trimethoprim and streptomycin resistances, harbour transposons which we designate Tn71 and Tn72. These transposons are indistinguishable from Tn7 in the resistances determined, in their molecular masses and in the number and relative positions of their sites susceptible to the restriction enzymes EcoRI, HindIII and BamHI. We conclude that Tn7 has been naturally spread among plasmids.

Base Sequence↗
PubMed1976

Plasmid-determined beta-lactamase indistinguishable from the chromosomal beta-lactamase of Escherichia coli.

A plasmid, derived from a naturally occurring strain of Proteus mirabilis, conferred resistance to cephalosporins, apparently mediated by a beta-lactamase indistinguishable from that determined by the chromosomal gene of Escherichia coli K-12. There was evidence for a recombination event between the wild-type plasmid and a defective F factor (Fsp) in the Escherichia coli K-12 culture in which it was stored.

Cephalosporins↗
PubMed1976

Compatibility properties of R483, a member of the I plasmid complex.

R483, an I pilus-determining plasmid previously reported as belonging to a distinct incompatibility group Ibeta, proved to be an atypical Ialpha plasmid; in a growing culture, the degree of inhibition of replication of one Ialpha plasmid by the presence of another was not uniform within the Ialpha group.

Colicins↗
PubMed1976

Transposition of a deoxyribonucleic acid sequence encoding trimethoprim and streptomycin resistances from R483 to other replicons.

R483, a plasmid of the Ialpha incompatibility group, contained a deoxyribonucleic acid (DNA) sequence encoding resistance to trimethoprim (TpR) and streptomycin (SmR) that could be transposed to other replicons, i.e., to the Escherichia coli chromosome and to related and unrelated plasmids. Each transposition resulted in the acquisition by the recipient replicon of a segment of DNA of about 9 X 10(6) daltons, both resistance genes, but never the colicin Ia or pilus genes of R483. Transposition took place at a single chromosomal site between dnaA and ilv and did not suppress the DnaA phenotype, in contrast to integration of the whole R483 plasmid. The chromosome, having received the transposition, could secondarily act as a transposition donor to another plasmid. Such a plasmid was indistinguishable from one having received a direct transposition from R483. TpR SmR transposition was very site specific and did not require a functional recA+ gene. We postulate that the TpR SmR segment of R483 is a transposon (TnC) with specific boundary sequences.

Base Sequence↗
PubMed1976

Characterization of SmSu plasmids by restriction endonuclease cleavage and compatibility testing.

Twelve plasmids carrying genes for streptomycin and sulfonamide resistance were studied for the number and distribution of sites on the plasmid moleucles susceptible to cleavage by the restriction endonuclease EcoRI. Ten of the twelve were found to have a single cut site, one plasmid (R678) had three such sites, and plasmid PB165, which was isolated as three supercoiled deoxyribonucleic acid species with molecular weights 7.4 x 10(6), 14.7 x 10(6), and 21.4 x 10(6) was reduced to a single (linear) species of molecular weight 7.6 x 10(6) after cutting with EcoRI. We conclude that PB165 forms oligomers in Escherichia coli and that the number of copies of these per chromosome is more consistant and that the number of copies of these per chromosome is more consistent with a negative than a positive control mechanism for plasmid replication. Compatibility testing of a positive control mechanism for plasmid replication. Compatibility testing of these plasmids showed they all belong to the same incompatibility group, which we designate IncQ, suggesting that they may have come from a common ancestor.

DNA Restriction Enzymes↗
PubMed1975

Compatibility properties of P1 and PhiAMP prophages.

Although phages P1 and PhiAmp are heteroimmune (Chesney and Scott, 1975 and Yarmolinsky, unpublished), their plasmid prophages are incompatible. Thus, the immunity and compatibility systems are two distinct regulators of phage replication. The two prophages, and plasmid P15B (Ikeda, Inzuka and Tomizawa, 1970) constitute a new compatibility group, designated Y.

Centrifugation, Density Gradient↗
PubMed1975

Assay of deoxyribonucleic acid homology using a single-strand-specific nuclease at 75 C.

We investigated the conditions under which a crude preparation of endonuclease S1 gives maximal hydrolysis of denatured deoxyribonucleic acid (DNA) while giving minimal hydrolysis of native DNA. The hydrolysis was measured by filtering and determining the acid-insoluble reaction product using 3H-labeled substrates. We also investigated various parameters in making this measurement. Under appropriate conditions (in 1 mM ZnSO-4, 0.168 M NaCl at pH 4.8) denatured DNA is hydrolyzed within 3% of completion whereas native DNA is essentially unaffected. The reaction was applied to assay plasmid DNA homoand heteroduplexes for which the method proves to be simple, fast, and reproducible.

Aspergillus↗
PubMed1974

Comparison of the deoxyribonucleic acid molecular weights and homologies of plasmids conferring linked resistance to streptomycin and sulfonamides.

Bacterial strains showing linked resistance to streptomycin (Sm) and sulfonamides (Su) were chosen representing a wide taxonomic and geographical range. Their SmSu resistances were transferred to Escherichia coli K-12 and then plasmid deoxyribonucleic acid (DNA) was isolated by ethidium bromide CsCl centrifugation. The plasmid DNA was examined by electron microscopy and analyzed by sedimentation through 5 to 20% neutral sucrose gradients. Plasmid DNA from strains having transmissible SmSu resistance consisted of two or three molecular species, one of which had a molecular mass of about 5.7 Mdal (10(6) daltons), the others varying between 20 to 60 Mdal. By using transformation or F' mobilization, we isolated the SmSu-resistance determinant from any fellow resident plasmids in each strain and again isolated the plasmid DNA. Cosedimentation of each of these with a differently labeled reference plasmid DNA (R300B) showed 9 out of 12 of the plasmids to have a molecular mass not significantly different from the reference (5.7 Mdal); two others were 6.3 and 9.2 Mdal, but PB165 consisted of three plasmids of 7.4, 14.7, and 21.4 Mdal. Three separate isolations of the SmSu determinant from PB165 gave the same three plasmids, which we conclude may be monomer, dimer, and trimer, respectively. DNA-DNA hybridizations at 75 C demonstrated 80 to 93% homology between reference R300B DNA and each isolated SmSu plasmid DNA, except for the 9.2-Mdal plasmid which had 45% homology and PB165 which had 35%. All the SmSu plasmids were present as multiple copies (about 10) per chromosome. The conjugative plasmid of R300 (present as 1.3 copies per chromosome) has been shown to have negligible effect on the number of copies of its accompanying SmSu plasmid R300B. We conclude that the SmSu plasmids are closely related and probably have a common evolutionary origin.

Carbon Radioisotopes↗