Unique insertion site of Tn7 in the E. coli chromosome.

Abstract

Among transposable elements, transposon Tn7 is unusual in that it inserts into a particular site of the Escherichia coli chromosome with high efficiency1,2 and with a unique orientation2. Most other transposable elements in prokaryotes are capable of translocating from and to a variety of sites in bacteriophage and plasmid DNA as well as in the chromosome3. We have previously shown that the ‘attachment site’ for Tn7 in E. coli is located between oriC and glmS at minute 82 (ref. 4) of the chromosome2. We now report the DNA sequences of the termini of Tn7, of the attachment site (before and after Tn7 insertion) and of an alternative site of Tn7 attachment. We conclude that the specificity of the attachment site is determined by specific DNA sequences and that secondary structures may be involved.