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P M Bennett

Publications and source records attributed to P M Bennett.

At least 109 records · Page 6Linked to original sources
PubMed1985

Characterization of Tn3926, a new mercury-resistance transposon from Yersinia enterocolitica.

A new transposon coding for mercury resistance (HgR), Tn3926, has been found in a strain of Yersinia enterocolitica, YE138A14. The element has a size of 7.8 kb and transposes to conjugative plasmids belonging to different incompatibility groups. A restriction map has been established. DNA-DNA hybridization indicates that Tn3926 displays homology with both Tn501 and Tn21; the greatest homology is shown with the regions of these transposons that encode HgR. Weaker homology is observed between Tn3926 sequences and those regions of Tn501 and Tn21 that encode transposition functions. Complementation experiments indicate that the Tn3926 transposase mediates transposition of Tn21, albeit somewhat inefficiently, but not of Tn501, while the resolvase mediates resolution of transposition cointegrates formed via Tn21, Tn501, or Tn1721.

Base Composition↗
PubMed1985

Evolution of an R plasmid from a cryptic plasmid by transposition of two copies of Tn1 in Providencia stuartii.

Examination of a series of isolates of Providencia stuartii collected over an 18 month period from a chronic-care patient at Bristol Royal Infirmary revealed the emergence of resistance to carbenicillin. Resistance was mediated by a 47 kb plasmid which transferred by conjugation to a plasmid-free strain of P. stuartii but not to Escherichia coli. Carbenicillin-sensitive isolates were either plasmid-free or contained a 36 kb cryptic plasmid. Restriction endonuclease mapping of this plasmid showed it to be closely related to 32 kb and 34 kb cryptic plasmids reported previously in P. stuartii from Bristol. Mapping of the R plasmid showed it to be derived from the 34 kb cryptic plasmid by transposition of two copies of Tn1.

Conjugation, Genetic↗
PubMed1985

Plasmid fusions mediated by one end of TnA.

We have observed plasmid fusions in a recA background mediated by a single end of TnA. These occur when transposase is provided either in cis or in trans. Insertions of the plasmid carrying the TnA inverted repeat sequence occur at many sites in the target plasmid. The point of fusion on the plasmid carrying TnA sequences always appears to be located in the region which carries the TnA inverted repeat sequence. In contrast to the transposition of an intact TnA element, plasmid fusions mediated by one end of TnA are very rare events. The implications of our results for models of transposition are discussed.

Chromosome Mapping↗
PubMed1984

Molecular organization of paramyosin in the core of molluscan thick filaments.

An arrangement of paramyosin molecules in the polar part of molluscan thick filaments is proposed which accounts for the X-ray diffraction pattern of the smooth adductor muscle (other than the part ascribed to actin) and for the appearance of separated filaments in the electron microscope. The proposed structure is based on the PI arrangement of Cohen et al. (1971), and contains sets of parallel, equidistant molecules with successive molecules displaced along the molecular axis by 72 nm, which we call PI sheets. Every molecule belongs to two PI sheets which are nearly perpendicular. This array is not propagated throughout the filament, but is sheared periodically in the direction of the molecular (filament) axis by 2/5 X 72 nm. The shear occurs along parallel equidistant planes which are inclined to the PI sheets. The analysis of the X-ray data has been made possible by concentrating on those patterns from filaments in which the two sets of PI sheets appear to be mutually perpendicular, a condition brought about by bathing the muscle in aqueous acetone. In one set, there are four intermolecular spaces between shear planes (this appears to be true at least for the smooth adductors of Ostrea edulis, Crassostrea angulata and Mercenaria mercenaria). In the other set, the number varies with species and probably lies between eight and ten in the first two and appears to be six in the last named species. The known paracrystalline nature of paramyosin filaments suggests that this number, though dominant in one species, is not exactly constant.

Animals↗
PubMed1984

"Splicing" of paramyosin filaments.

We have obtained electron micrographs of negatively stained thick filaments from the smooth adductor muscles of the oyster which show in detail the bipolar region of the paramyosin core. The polarity of the filament changes to either side of a line included at only 3 degrees to the filament axis. Along this line the pattern of interactions repeats every 8 X 14.4 nm. A model for the molecular organization is proposed. We conclude that this unusual arrangement occurs in order to maintain the tensile strength of the filament in the same way as the strength of a rope is maintained when joining two ends by a long splice.

Animals↗
PubMed1984

Cryptic plasmids in hospital isolates of Providencia stuarti.

The distribution of cryptic plasmids among 123 isolates of Providencia stuarti from a hospital ward during a prospective epidemiological study is reported. Two closely related stable plasmids (34 Kb and 36 Kb) were identified by restriction endonuclease digest analysis of plasmid DNA. One or other of these cryptic plasmids was carried by 40 isolates, the remainder were plasmid-free. A higher proportion of one cryptic plasmid (CPT-A) was found in environmental isolates than in isolates from patients. The serotype of all isolates of P. stuarti was O63 and they were epidemiologically related. Two of the eight patients colonised by P. stuarti carried all three possible variants: plasmid-free (PFI) strains or strains containing cryptic plasmid A (CPT-A) or cryptic plasmid B (CPT-B). The epidemiological significance of these results is discussed.

Aged↗
PubMed1983

R46 encodes a site-specific recombination system interchangeable with the resolution function of TnA.

Transposition of Tn4 onto the IncN plasmic R46 generates unstable DNA molecules. The R46::TnA recombinant plasmids undergo further DNA rearrangements which depend on the orientation in which the TnA element is inserted into the plasmid, and deletions and inversions of R46 and TnA sequences have been observed. Both types of rearrangement have the same specific endpoints, one within TnA and one located between the R46 coordinates, 36.0 and 37.0. The results are consistent with the operation of a recA-independent, site-specific recombination system utilizing, at least in part, the transposon cointegrate resolution system of TnA, together with R46-encoded functions. Data are presented that indicate that R46 encodes analogs of both the res site of TnA and its tnpR gene, although little homology between this element and the plasmid is apparent. Models for the TnA-induced generation of site-specific deletions and inversions upon transposition of TnA to R46 are presented.

Chromosome Deletion↗
PubMed1982

Penicillinase-producing Neisseria gonorrhoeae: a molecular comparison of 5.3-kb and 7.4-kb beta-lactamase plasmids.

Restriction endonuclease analysis and heteroduplex studies indicate that the only difference between the 5.3-kilobase (kb) and 7.4-kb plasmids from beta-lactamase-producing Neisseria gonorrhoeae is that the latter is the 5.3-kb plasmid with a 2.1-kb insertion. The insertion is bounded by inverted repeats of approximately 300 base pairs. Several plasmids from beta-lactamase-producing N. gonorrhoeae isolated at different times and in different countries were compared. Nine 5.3-kb plasmids were examined and found to be indistinguishable, as were sixteen 7.4-kb plasmids.

Base Sequence↗
PubMed1982

Structure of the thick filaments in molluscan adductor muscle.

Molluscan adductor muscles are in general of two kinds--a slow-acting smooth muscle, which after contraction can go into a catch state, in which tension is maintained for many hours with a small turnover of ATP, and a quicker-acting muscle, usually to some extent striated, which has not the catch property in marked degree, if at all. The thick filaments of both kinds of adductors contain myosin and paramyosin. Those from catch muscles are noteworthy for their high paramyosin content(up to about 90% by weight), which may be correlated with their great length and diameter. The paramyosin forms a core with a surface layer of myosin. Recently, we have shown that the paramyosin core of catch muscles resembles a single crystal in its molecular arrangement, although the degree of regularity varies from one filament to another. The evidence is from electron microscopy both of individual filaments and of pieces of whole muscle embedded and sectioned. Individual negatively stained filaments change greatly in appearance when rotated round their long axes, in a way not compatible with a helical structure. A three-dimensional reconstruction of the filament from micrographs of a rotated filament confirms this. Transverse sections of smooth adductor muscles show no internal features within the thick filaments when viewed accurately along the filament axis. On tilting striations appear on the filaments that may be correlated with the planes of the Bear-Selby net. They are a general feature of the filaments and have been seen in the smooth adductors of P. maximus, O. edulis, Crassostrea gigas, M. mercenaria, of the anterior byssus retractor of M. edulis and in the red (obliquely striated) adductor of M. mercenaria. The arrangement of the myosin on the paramyosin core is not known.

Animals↗
PubMed1981

The structure of the paramyosin core in molluscan thick filaments.

The thick filaments of molluscan muscles have been examined by electron microscopy and X-ray diffraction in order to test whether the structure of the paramyosin core is crystalline and not helicoidal. In accurately cut transverse sections of the white adductor muscle of the oyster the thick filaments are uniformly stained but, when the sections are titled, parallel striations are revealed. Essentially all the filaments can be shown to exhibit striations which can only be explained in terms of a crystalline structure. The crystallinity is, however, not perfect since the striations although often straight are more frequently curved. Two sets of striations of different spacing can be detected in each filament on tilting to either side of the filament axis. Their spacings when compared to the Bear-Selby net a spacing obtained from X-ray diffraction patterns of the embedded muscle indicate that the striations are seen when the filaments are viewed down the 201 and 301 planes of the Bear-Selby net. Striations have been observed in thick filaments from other catch muscles, the white adductor of the clam, the smooth adductor of the scallop and the anterior byssus retractor of the mussel as well as in a non-catch muscle, the red adductor of the clam. In all cases the spacing striations was similar indicating that, contrary to previous reports, when the conditions are the same the a spacing of the Bear-Selby net is approximately constant from one muscle to another and hence that the paramyosin structure in all these muscles is similar.

Animals↗