M. H. Richmond

Transposition of TnA Does Not Generate Deletions

SummaryWe 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.

Characterisation of Tn501, a transposon determining resistance to mercuric ions

SummaryThe transposon encoding resistance to mercuric ions, Tn501, is 5.2 (±0.1)×106 daltons and is bounded by small inverted repeats. The restriction sites for the restriction endonucleases EcoRI, HindIII and SalGI have been mapped on the element.

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

SummaryThe 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.

A restriction enzyme map of R-plasmid RP1

Abstract The relative positions of the sites on RP1 of the following restriction enzymes were mapped: EcoRl, BamH1, HindIII, BglII, SmaI, and PstI.

The transposons Tn 501 (Hg) and Tn 1721 (Tc) are related

Internal sequences of Tn 501 (Hg) and Tn 721 (Tc) have been compared by hybridization. In spite of the difference in the resistance they code for, there is extensive homology between the two elements. This homology resides in the transposon-coded genes that are necessary for transposition and indicates that the elements are closely related.

The Location of Sequences of TnA Required for the Establishment of Transposition Immunity

SummaryA sequence of TnA, at the end of TnA distal to the bla gene, is required for the establishment of transposition immunity. This sequence is always necessary but is not always sufficient for the establishment of transposition immunity.

The stable carriage of two TnA units on a single replicon

SummaryBacterial plasmids which contain a copy of TnA are refractory 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 plasmids containing two copies of TnA carried the transposons in opposite orientation.

The tnpR gene product of TnA is required for transposition immunity

SummaryA mutant of TnA no longer recognizing immune plasmids has been isolated. The mutation is complemented in trans by a functional tnpR gene. The requirement for wild type tnpR gene product for the establishment of transposition immunity was confirmed by the use of a derivative of transposon Tn3 in which both the tnpA and the tnpR genes are partly deleted. This deleted Tn3 was shown to transpose onto an immune plasmid in the presence of a wild type tnpA gene but not in the presence of both tnpA and tnpR genes.

The inactivation of tet genes on a plasmid by the duplication of one inverted repeat of a transposon-like structure which itself mediates tetracycline resistance

Abstract Derivatives of a naturally occurring IncFII tetracycline resistance plasmid (pUB889) which are unable to confer resistance to tetracycline, and which were isolated from both partners of a married couple, have been examined. The tet genes are part of a transposon-like structure which is closely related to, but distinct from, Tn10. The lesions in the two plasmids examined are identical and involve the insertion of a nucleotide sequence of 0.9 × 106 within the region encoding tetracycline resistance, expression of which is lost as a consequence. The extra DNA is homologous with the nucleotide sequence, a pair of which form the inverted repeats of the Tn10-like structure. We conclude that this nucleotide sequence comprises an IS element. The epidemiological implications arising from the origin of these plasmids are discussed.

Persistence and spread of a chloramphenicol resistance-mediating plasmid in antigenic types of Escherichia coli, pathogenic for piglets

All chloramphenicol-resistant Escherichia coli strains isolated from piglets in the State veterinary Serum Laboratory, Copenhagen, in 1974-1975 harbored plasmids of IncFII group with largely the same resistance markers. Two strains from 1978 carried plasmids with similar characters. Restriction enzyme analysis of DNA from these plasmids with restriction endonucleases EcoRI, BglII, and PstI shows that the Cm plasmids are extremely closely related; but the patterns obtained (particularly from PstI digests) enable the classification of the plasmids into groups. These bear a strong relation to time and place of isolation so that plasmids isolated on the same farm belong to the same group even when their host strains are of different antigenic types. It is concluded that these plasmids have evolved from a single plasmid.