Precise excision of bacterial transposon Tn 5 in yeast

We have demonstrated that precise excision of bacterial transposon Tn 5 can occur in the yeast, Saccharomyces cerevisiae. Tn 5 insertions in the yeast gene LYS2 were generated by transposon mutagenesis made in Escherichia coli by means of a λ::Tn 5 vector. Nine insertions of Tn 5 into the structural part of the yeast LYS2 gene situated in a shuttle epsiomal plasmid were selected. All the plasmids with a Tn 5 insertion were used to transform yeast strains carrying a deletion of the entire LYS2 gene or a deletion of the part of LYS2 overlapping the point of insertion. All insertions inactivated the LYS2 gene and were able to revert with low (about 10^-8) frequencies to lysine prototrophy. Restriction analysis of revertant plasmids revealed them to be indistinguishable from the original plasmid without Tn 5 insertion. DNA sequencing of the regions containing the points of insertions, made for two revertants, proved that Tn 5 excision was completely precise.