The E. coli K-12 chromosome flanked by two IS10 sequences transposes

Properties of new Escherichia coli Hfr strains constructed by integration of pSC101-derived conjugative plasmids

Conjugative temperature-sensitive plasmids were derived from pSC101. These plasmids are useful in genetic analysis for two reasons: (i) they render possible the construction of new Hfr lines by plasmid integration at predetermined chromosomal loci via Tn10 inverse transposition, and (ii) the Hfr characters are transducible via bacteriophage P1. We also showed that replication from pSC101 origin is deleterious for the plasmid-chromosome fusion.

A simple procedure for transferring genes cloned in Escherichia coli vectors into other gram-negative bacteria: phenotypic analysis and mapping of TOL plasmid gene xylK

A simple method to transfer non-conjugative Escherichia coli plasmids to other Gram-negative bacteria and their maintenance is described. This method involves generation of inverse transposition-mediated cointegrates of the non-conjugative E. coli plasmid with a conjugative IncW broad-host-range plasmid, R388, carrying Tn10. Isolation of such cointegrates was readily effected by conjugal transfer from an E. coli donor containing the two plasmids to an E. coli recipient, with selection for transconjugants expressing a marker of the E. coli plasmid. This method is particularly useful when large series of E. coli vector-based clones need to be expressed in other Gram-negative bacteria to be functionally analysed, either by complementation or recombination. Utility of the method is shown by a functional analysis in Pseudomonas putida of pBR322 hybrid plasmids containing catabolic genes of TOL plasmid pWW0.

Genetic evidence that Tn10 transposes by a nonreplicative mechanism

We present genetic evidence that the tetracycline resistance element Tn10 transposes by a nonreplicative mechanism. Heteroduplex Tn10 elements containing three single base pair mismatches were constructed on lambda phage genomes and allowed to transpose from lambda into the bacterial chromosome. Analysis of TetR colonies resulting from such transpositions suggests that information from both strands of the transposing Tn10 element is transmitted faithfully to its transposition product. The simplest interpretation of these results is that the transposing element is excised from the donor molecule and inserted into the target molecule without being replicated. A mismatch 70 base pairs from one end of the transposon is preserved, suggesting that there is little or no replication, even at the termini of the element, during transposition in vivo.

Transposition behavior of IS15 and its progenitor IS15-delta: are cointegrates exclusive end products?

We report that the major product of IS15-promoted transposition is a cointegrate. When present in the multicopy plasmid pBR322, IS15 and its progenitor IS15-delta mediate the formation of cointegrates at frequencies of 3.5 X 10(-4) and 2.9 X 10(-5), respectively. We have studied the stability of the cointegrates generated by IS15 and IS15-delta. While these structures are resolved in a rec+ host, they were stable in a rec- host. These observations suggest that neither IS15 nor IS15-delta encode a resolvase and that cointegration is an end product of their transposition process. These properties of IS15-delta and IS15 can explain the transitions from IS15-delta to IS15 and from IS15 to IS15-delta observed in vivo.