RECOMBINATIONAL MECHANISM OF IS50 MOBILE ELEMENT PRECISE EXCISION IN ESCHERICHIA-COLI K12 CELLS

Precise excision of Tn10 type composite transposon proceeds according to the slippage mechanism An alternative recombinational pathway appea red to be possible for excision of Tn9-type transposons flanked by IS elements in direct orientation. Using experimental system containing T n5 or its IS50 module inserted into a E. coli plasmid, that this trans poson could also undergo precise excision via the recombination mechan ism. Recombination occurs in trans between short direct repeats of the transposon, resulting in formation of a specialized dimer of the pare ntal plasmid and does not depend upon transposase and RecA integrity. Introduction of a replication origin into the mobile element results i n domination of the excision-by- recombination mechanism even for tran sposons with long inverted terminal repeats. This is probably due to s uppression of the slippage mechanism.