Packaging of an oversize transducing genome by Salmonella phage P22

Transposable genetic elements and plasmid evolution

Transposable elements of DNA that are structurally defined and genetically discrete units seem to have an important role in the evolution of bacterial plasmids. Recombination occurring at the termini of such elements can result in the joining together of unrelated DNA segments that lack extensive nucleotide sequence homology. In addition, transposable elements serve as novel biological switches capable of turning on and off the expression of nearby genes as a consequence of their insertion into or excision from plasmid genomes.

Isolation of inverted repeat sequences, including IS1, IS2, and IS3, in Escherichia coli plasmids

A method is described for isolation of inverted repeat DNA sequences that occur in E. coli plasmids. The procedures of the isolation involved: (a) denaturation of intact plasmid DNA, (b) a rapid, 30 sec, renaturation of inverted-repeat sequences in the genome, (c) digestion of the single-stranded portion by S1 nuclease to recover duplex DNA, and (d) detection and purification of the duplexes using 1.4% agarose gel electrophoresis. If a plasmid DNA carried inverted repeats of either one type or two different types of special DNA sequences, these procedures enabled us to observe either one or two characteristic DNA bands, respectively, in the agarose gels. If a plasmid DNA did not carry any inverted repeats, or if the plasmid DNA only carried direct repeat sequences, no characteristic DNA bands were recovered. Cleavage of the spacer DNA between inverted repeat sequences generated no gel bands. This indicated that the inverted repeat sequences must be in the same strand. Using this method, we isolated and purified several repeated sequences, including IS1, IS2, and IS3, from derivatives of F and R plasmids.

Acquisition of a determinant for chloramphenicol resistance by coliphage lambda

A determinanat for chloramphenicol resistance, cam, initially detected on a resistance transfer factor (RTF) and since transferred to phage P1, may be acquired from P1 by coliphage lambda. Lambdapcam are obtained when a lambda prophage is induced in bacteria which also harbor P1 cam prophage. Lambdacam formation is not dependent upon host Rec or lambda Red recombination functions. Electron microscopic heteroduplex analysis shows that the cam locus in two lambdapcams is a 5% addition of DNA in the b2 region of lambda, not contiguous with att. The extent and nucloetide sequence of the DNA insertion in the two independent lambdapcam isolates appear to be the same though they are located at different sites within the b2 region. We conclude that the determinant for chloramphenicol resistance is contained on a unique piece of DNA which facilitates its insertion into a number of unrelated genomes.

Translocation of the tetracycline resistance determinant from R100-1 to the Escherichia coli K-12 chromosome

Pairs of normally incompatible derivatives of R100-1 (one ChlS TetR, the other ChilR TetS) were forced to coexist in a recA host by selection for ChlR TetR cells. After many generations stable derivatives were isolated. The analysis of none independent stabilization experiments showed that in each case TetR was translocated from the plasmid to the chromosome of the host. No evidence for the joint integration of other plasmid genes (those controlling transfer, antibiotic resistance, incompatibility, or origin of transfer replication) was obtained. One of the chromosomal TetR determinants was mapped close to metE.

Isolation of a nontransmissible antibiotic resistance plasmid by transductional shortening of R factor RP1

A plasmid segregant carrying tetracycline and carbenicillin resistance markers has been isolated from R factor RP1 by transductional shortening with phage P22. The new plasmid RP1-S2, which has a molecular weight of 23 times 10-6, has lost the transfer, phage sensitivity, and neomycin resistance functions of RP1. It combines readily with a W group plasmid, R388, to form a transmissible carbenicillin and trimethoprim resistance plasmid, RWP1.

Electron microscope heteroduplex studies of sequence relations among bacterial plasmids: identification and mapping of the insertion sequences IS1 and IS2 in F and R plasmids

Heteroduplex experiments between the plasmid R6 and one strand of the deoxyribonucleic acid (DNA) of a lambda phage carrying the insertion sequence IS1 show that IS1 occurs on R6 at the two previously mapped junctions of resistance transfer factor (RTF) DNA with R-determinant DNA. From previous heteroduplex experiments, it then follows that IS1 occurs at the same junctions in R6-5, R100-1, and R1 plasmids. Heteroduplex experiments with the DNA from a lambda phage carrying the insertion sequence IS2 show that one copy of IS2 occurs in R6, R6-5, and R100-1 (but not R1) at a point within the RTF with coordinates 67.5 TO 68.9 kilobase units (kb). In an accompanying paper, Ptashne and Cohen (1975) show that the insertion sequence IS3 occurs on R6 and R6-5. R100-25, a traC mutant, differs from its parent R100-1 only in that it contains an additional copy of IS1 inserted within the tra gene region of 82.1 kb. R100-31, atraX, TC-s mutant of R100-1, is deleted in R100-1 sequences starting at one of the IS3 termini (46.9 kb) and extending with RTF to 61.0 kb. Heteroduplex studies of F plasmids with the DNA of a lambda phage bearing insertion sequence IS2 show that the sequence of F with coordinates 16.3-17.6F is IS2. The occurrence of IS1 at the two junctions of R-determinant DNA and RTF DNA in R plasmids provides a structural basis to explain the mechanism of the previously observed formation of molecules containing one RTF unit and several tandem copies of the R-determinant unit, when R plasmids in Proteus mirabilis are grown in the presence of antibiotics, and the segregation of an R plasmid into an RTF unit and an R-determinant unit. In general, correlation of our results with previous studies shows that insertion sequences play a role in a variety of F- and R-related intra- and intermolecular recombination phenomena.

Isolation and characterization of lambda transducing bacteriophages for argF, argI and adjacent genes

Two genes for ornithinetranscarbamylase exist in strain Escherichia coli K-12, argI, at 85 min, and argF, at 7 min. In an attempt to compare the deoxyribonucleic acid material of these two genes, the lambda transducing phages carrying a portion of the argI region, lambda dvalS argI, lambda pvalS, and lambda dvalS pyrB, and of the argF region, lambda dargF, have been isolated. Their structure, including that of phi 80dargF previously isolated, was studied by the method of heteroduplex mapping. In this paper, the results of this mapping are reported.

Origin of the TEM-beta-lactamase gene found on plasmids

A sequence of deoxyribonucleic acid of 2.7 times 10-6 to 3.3 times 10-6 daltons which includes the TEM beta-lactamase gene is present on the small plasmid RSF 1030 (R-Amp). This same sequence is present on plasmid derivatives that have received a translocation of deoxyribonucleic acid specifying the TEM beta-lactamase and is also present on naturally occurring plasmids of the F1, F11, N, X, O, I, C, and W incompatibility groups that do not specify ampicillin resistance or specify O-type beta-lactamases.