Tn7

The bacterial transposon Tn7 is a sophisticated mobile element that pursues several alternative lifestyles to promote its propagation. Tn7 was first isolated from a trimethoprim- and streptomycin-resistant bacterium in a calf that was being treated prophylactically with trimethoprim in its feed. The tns genes are all oriented in the same direction with their 5' ends toward the right end of Tn7. These genes were identified genetically by analysis of deletion and insertion derivatives of Tn7 and by gene sequencing, protein identification, and protein purification (TnsA, TnsB, TnsC, TnsD, and TnsE). The topological requirements of the donor DNA substrate have been examined in the in vitro Tn7 transposition system. The partial sequence of another TnsA gene distinct from the others has also been described, suggesting that more close relatives of Tn7 remain to be discovered. Transposons have long been useful tools for the manipulation of genes and genomes. The study of Tn7 has enriched the study of mobile DNA; there are distinct differences between Tn7 and other elements as well as similarities between Tn7 and other elements. The study of Tn7 seems sure to continue to provide an interesting system in which to examine the interaction of a transposable element with its host, to provide interesting problems in protein-DNA and protein-protein interactions to study, and to provide useful tools for the study and manipulation of genes and genomes.