[The recombination mechanism for precise excision of the IS50 mobile element in Escherichia coli K12 cells].

Precise excision of composite transposons of Tn10 type, with long inverted repeats, proceeds according to the slippage mechanism (Brunier et al. parallel Cell. 1988. V. 52. P. 883). An alternative recombinational mechanism proved to be possible for transposons with directly oriented IS elements (Goryshin et al. parallel Mol. Biol. 1991. V. 25. P. 614). Making use of an experimental system with plasmid localization of the Tn5 transposon or its IS50 module, we have shown that the recombination mechanism of precise excision can be realized for these mobile elements. The recombination occurs in-trans between direct short repeats flanking a transposon. Formation of a specialized dimer of the original plasmid takes place in this case. The recombination does not depend on the integrity of RecA protein or transposase. Integration of an ori of replication into the mobile element results in the domination of recombination mechanism of precise excision even if the transposon has long inverted repeats at its ends. This seems to occur as a result of inhibition of the slippage mechanism.