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P M Bennett

Publications and source records attributed to P M Bennett.

At least 19 recordsLinked to original sources
PubMed1979

In vitro formation of a complex between cytoskeletal proteins of the human erythrocyte.

The formation of a high-molecular weight complex between spectrin and F-actin depends on the presence of a third cytoskeletal constituent, protein 4.1. Electron microscopy shows that in this ternary complex the actin filaments are linked by bridges, which have the appearance of spectrin. The spectrin must be in the tetrameric state for such bridges to form: the dimer is evidently univalent, for it binds but forms no cross-links. G-actin also fails to form extended complexes. It is inferred that in the native cytoskeleton the spectrin is tetrameric and associated with 4.1 and probably oligomers of actin.

Actins↗
PubMed1979

Persistence of plasmid-carrying tetracycline-resistant Escherichia coli in a married couple, one of whom was receiving antibiotics.

This paper describes an extension to an earlier account of the coliform flora carried by a married couple, one of whom was taking tetracycline for prolonged periods. The latter phase of this study was notable for the following: first, certain tetracycline-resistant Escherichia coli O antigen types persisted in one of the participants for several weeks after tetracycline was withdrawn; second, a course of ampicillin led to replacement of the tetracycline-resistant flora by one that was ampicillin resistant, but the end of the ampicillin course led to the reappearance of the tetracycline-resistant line, even though no tetracycline was being taken; and third, the tetracycline-sensitive O75 E. coli, which appeared toward the end of the survey, had not lost their plasmid but carried a derivative in which the tetracycline resistance gene(s) had been inactivated by the insertion of an extra piece of deoxyribonucleic acid with a molecular weight of about 1 megadalton.

Antigens, Bacterial↗
PubMed1979

Sites of insertion of TnA and TnM in RP1 and its derivatives.

The sites of insertion of TnM into the plasmid RP1, into derivatives of RP1 lacking TnA, and into derivatives in which the location of TnA within RP1 has been altered, were determined. Similarly, the sites of insertion of TnA into derivatives of RP1 from which TnA had been deleted, both with and without copies of TnM, have been examined. These studies show the presence in the plasmids of 'hot-spots' for TnA and TnM insertion. It is clear from the observations, however, that a particular DNA sequence in the recipient replicon is not sufficient to definite a 'hot-spot' since particular sequences sometimes do, and sometimes do not, contain many sites of insertion for a given transposon.

Base Sequence↗
PubMed1979

The persistence of R-plasmid-carrying E. coli in a married couple, one of whom was receiving antibiotics.

The aerobic Gram-negative intestinal flora of two individuals, husband and wife, has been followed for about 20 months. The wife was receiving prolonged tetracycline treatment for acne during the first year of the study and was found to carry a large proportion of tetracycline resistant E. coli in her faecal flora even after the tetracycline treatment had ended. A brief therapeutic course of ampicillin during the period when no tetracycline was being taken resulted in the temporary disappearance of the tetracycline resistant flora, but this returned, even though no tetracycline was being taken, as soon as the ampicillin ended. The husband took no antibiotics during the period under study but was frequently found to excrete the same resistant E. coli as his wife. Moreover, the plasmids carried by the tetracycline resistant strains in the wife and the husband were often indistinguishable. This suggests that R-plasmids may spread from people under treatment to close relatives who have not been treated.

Ampicillin↗
PubMed1978

Regional preference of insertion of Tn501 and Tn802 into RP1 and its derivatives.

The sites of insertion of Tn501 into RP1 and into derivatives of this plasmid that either lack the Tn801 (TnA) element or contain it in a different location have been determined. Similarly, the sites of insertion of Tn802 into a derivative of RP1 that lacks the Tn801 element and into recombinants of this plasmid with Tn501 were determined. 'Hot spots' for insertion were observed with both transposons; but it is clear that a particular DNA sequence is not sufficient to define a 'hot spot', since a particular region does contain many insertions when present in one plasmid but does not do so when part of another.

Base Sequence↗
PubMed1978

The stable carriage of two TnA units on a single replicon.

Bacterial plasmids which contain a copy on TnA are refactory to the uptake of a second by transposition. However plasmids containing two such copies can be constructed by in vitro recombination techniques. Some plasmids containing two copies of TnA have been obtained by conventional transposition, but in all cases they arose by the virtually simultaneous insertion of both units into a replicon that carried no TnA. All stable plamids containing two copies of TnA carried the transposons in opposite orientation.

DNA Replication↗
PubMed1977

Transposition of TnA does not generate deletions.

We have examined the incidence of loss of the TnA unit, Tn801, from RP1 under conditions where transposition of Tn801 to another replicon. R388, was readily detected. We found that the frequency of transposition of Tn801 from RP1 to R388 exceeded, by at least a factor of one hundred, the frequency at which it was deleted from RP1. We conclude that, in general, transposition of Tn801 does not generate derivatives of the donor plasmid which specifically lack Tn801. The relevance of these findings to the mechanism of transposition is discussed.

Chromosome Aberrations↗
PubMed1977

Spread of a single plasmid clone to an untreated individual from a person receiving prolonged tetracycline therapy.

The aerobic gram-negative intestinal flora of two individuals living in close proximity was followed for 17 months. One of these persons was receiving a prolonged tetracycline treatment for acne vulgaris and was colonized by tetracycline-resistant Escherichia coli strains throughout the survey. The other person studied received no antibiotics during the period in question, but was frequently found to excrete a number of E. coli strains harboring tetracycline-resistant plasmids. The two E. coli strains (O75.H7 and O23.H16) excreted from both persons most frequently were indistinguishable, and so were the R-plasmids they carried. This suggests that R-plasmid-carrying E. coli may spread from individuals under treatment to close relatives that have not been treated.

Bacteriophage Typing↗
PubMed1977

Inhibition of TnA translocation by TnA.

Plasmids already containing TnA showed decreased susceptibility to the translocation of a further TnA unit when compared with related plasmids that did not contain TnA. The translocation immunity imposed by TnA is exerted only on the plasmid of which it is part. It is suggested that this desensitization by a translocation unit is a general phenomenon that reduces the mutational effects of translocation.

Ampicillin↗
PubMed1977

Characterization of a translocation unit encoding resistance to mercuric ions that occurs on a nonconjugative plasmid in Pseudomonas aeruginosa.

The nonconjugative plasmid, pVS1, has a molecular weight of 18.5 X 10(6) and confers resistance to sulfonamides and to mercuric ions. In Pseudomonas aeruginosa PAO, the transfer can be mobilized by a variety of conjugative plasmids, and the process does not require a functional recombination system in the donor. Hybrid plasmids that arise by the relocation of the mer gene onto the mobilizing plasmid can be isolated readily, and, as far as can be determined, these hybrids retain the genome of the conjugative plasmid in toto. The relocation of mer occurs by a Rec-independent process and leads to a constant increase (about 6 X 10(6) daltons) in the size of the recipient plasmid. This suggests that the mer gene in pVS1 is located on a translocation unit, designated Tn501, of a molecular weight of about 6 X 10(6). The translocation of Tn501 into RP1 is not usually associated with the loss of any known plasmid-mediated function, but transfer-defective or tetracycline-sensitive derivatives do occur at frequencies of about 4%, whereas carbenicillin-sensitive or kanamycin-sensitive variants arise with a frequency of about 0.2% each. It seems therefore that the integration of Tn501 can occur at any one of a minimum of five sites in RP1.

Conjugation, Genetic↗
PubMed1977

Properties of derivatives of the Pseudomonas plasmid pVS1 that have inherited carbenicillin resistance from RP1.

A procedure is described for the isolation, in Pseudomonas aeruginosa PAO, of bacteria carrying derivatives of pVS1 that inherited the carbenicillin-resistance determinant from RP1 either alone or together with that for aeruginocin resistance. Such bacteria occur among the transconjugant progeny from both recombination-proficient or -deficient pVS1+ RP1+ donors, suggesting that the formation of these plasmids is due to the translocation of TnA from RP1 into pVS1. It is possible, therefore, that the aeruginocin-resistance determinant is part of TnA or is closely linked to it. Unexpectedly, none of these plasmids showed the 3 x 10(6)- to 4 x 10(6)-dalton increase in size predicted for TnA+ derivatives of PVS1. It is suggested that an interaction between TnA and the Tn501 translocation unit in pVS1 could account for this result.

Anti-Bacterial Agents↗
PubMed1976

Isolation and characterisation of deletion mutants involving the transfer genes of P-group plasmids in Pseudomonas aeruginosa.

The P-group plasmids RP1 and R26 are recovered at low frequency following conjugal transfer to B3-lysogens of P. aeruginosa PAO. The rare carbenicillin-resistant transcipients that do arise are usually transfer-defective (Tra-) and may show the loss of other plasmid borne functions, namely kanamycin-resistance (Kmr) and reduced plating of phage G101 (Spp+). The four phenotypic classes that occur among the Tra- derivatives are respectively, Tra- (69-81%), Tra- Spp- (12-30%), Tra- Kms and Tra- Kms Spp- (0.2-1%), of which the latter three are dut to plasmid deletions. This is seen from the sizes of the plasmids carried by these bacteria and from the transductional analysis of the R26-derivatives. Thus, although R26 (MW = 52 X 106 daltons) is too large to be transduced by phage F116L (MW = 40 X 106), this is possible for its Tra- Kms and Tra Kms Spp- derivatives. The phenotypes and frequencies of the various transcipient classes suggests that the gene order Km.. Tra.. Spp occurs in both RP1 and R26, and that Spp is more closely linked to Tra than is Km. These conclusions are supported by the sizes of the plasmid mutants since deletions spanning the loci Km Tra Spp, Km Tra, and Tra Spp involve the loss of DNA of MW 8-17 X 106, 5-13 X 106 AND 1-9 X 106 DALTONS RESPECTIVELY. Whilst all the transcipients displayed the incompatibility properties of the parent plasmids (Inc+), only some retanied plasmid surface exclusion (Sfx+). Moreover, a strict correlation existed between the Sfx and Spp phenotypes such that the transcipients were either wild type, Sfx- Spp-, or displayed an intermediate phenotype for both characters. Thir are different manifestations of the same gene function. The deletion map of these various markers in both RP1 and R26 therefore seems to be Km.. Tra.. Sfx/Spp.. Inc.

Bacteriophages↗
PubMed1976

The properties of hybrids formed between the P-group plasmid RP1 and various plasmids from Pseudomonas aeruginosa.

R38, R931-1, and R933 are conjugative plasmids derived from strains of Pseudomonas aeruginosa. They confer resistance to mercuric ions (Hg-r), and do not tranfer from P. aeruginosa to Escherichia coli at detectable frequencies. Hybrids between each of these plasmids and the P-group plasmid, RP1, have been detected among the rare Hg-r transconjugants arising from matings of P. aeruginosa PAO donors (RP1 + R+) and E. coli K12 recipients. Two independently isolated hybrid plasmids from each of the three mating combinations have been studied. All were found to confer the entire marker phenotype of RP1, but only the Hg-r phenotype of their second parent. Moreover, all were larger than RP1 but comprised only two groups of sizes; those increased by about 14 x 10(6) daltons (the RP1/R38 hybrids), and those increased by about 30 x 10(6) daltons (the RP1/R931-1 and RP1/R933 hybrids). The hybrid plasmids were all too large to be transduced intact by phage F116L, but tranduction of fragments was possible. Thus, the determinants for both carbenicillin-resistance (Cb-r) (from RP1) and mercuric-ion-resistance could be "rescued" by recipients that already carried an RP1-like plasmid and were recombination-proficient. A molecular analysis of the plasmids recovered from such transductants suggested that each of the parental hybrids was comprised of an entire RP1 genome into which a fragment of heterologous DNA had been inserted. In similar experiments in which the recipient carried a derivative of R931-1, the Hg-r but not the Cb-r determinant could be rescued. This suggested that R38, R931-1, and R933 shared sufficient homology in the region of the mer gene for recombination to occur between them. The reason for the inability to rescue the Cb-r determinant was also investigated.

Chromosome Mapping↗
PubMed1976

A molecular analysis of transductional marker rescue involving P-group plasmids in Pseudomonas aeruginosa.

The molecular properties of the P-group plasmids R26, R527 and R18-18- (a carbenicillin-sensitive derivative of R18) have been compared with those of RP1. R18-18 and RPI have a MW about 38 X 10(6) daltons, and R26 and R527 of 52 X 10(6) daltons (determined from contour lengths). All three plasmids have a bouyant density similar to that of RPI (1.719 g/cm3, 60% GN. From their molecular and phenotypic similarities, these plasmids probably represent two pairs of identical or closely similar elements. Resistant bacteria are not recovered following F116L-mediated transduction of R26 (or R527), and this correlates with the plasmids' larger size (phage genome=40 X 10(6) daltons). Fragments of R26 are, however, transduced and their resistance determinants may be "rescued" by recombination if the recipient harbours R1818. Such events are accompanied by an increase in the size of the recipient plasmid from 38 X 10(6) to 52 X 10(6) daltons following inheritance of the resistance determinants Sm Su Gm Hg, but not Cb. Thus, Sm Su Gm Hg are encoded in a DNA segment of MW about 14 X 10(6) daltons which apparently has no homologous region on R18-18. Since a piece of DNA of this MW also corresponds to the difference in size between R26 and R18-18, it is possible that the former is derived from an RPI-like element which has acquired these additional resistance determinants.

Carbenicillin↗