The bacterial transposon Tn 5 inserts into dozens of sites in a gene, some of which are used preferentially (hotspots). Features of certain sites and precedents provided by several other transposons had suggested that sequences in target DNA corresponding to the ends of Tn 5 or of its component IS 50 elements might facilitate transposition to these sites. We tested this possibility using derivatives of plasmid pBR322 carrying IS 50 I or O end sequences. Tn 5 inserted frequently into an IS 50 I end at the major hotspot in pBR322, but not into either an I end or an O end 230 by away from this hotspot. Adenine (dam) methylation at GATC sequences in the I end segment interferes with its use as the end of a transposon, but a dam- mutation did not affect Tn 5 insertion relative to an I end sequence in target DNA. These results support models in which the ability of Tn 5 to find its preferred sites depends on several features of DNA sequence and conformation, and in which target selection is distinct from recognition of the element ends during transposition.
- Insertion sequence
- dam methylation