Autonomous and non-autonomous Tn 3 -family transposons and their role in the evolution of mobile genetic elements.

The Tn 3 family of transposons includes diverse elements that encode homologous transposases and contain conserved terminal inverted repeat sequences (IRs). The recent identification of non-autonomous elements, named TIMEs (Tn 3 -derived Inverted-repeat Miniature Elements), has shed new light on the diversity and evolution of this transposon family. A common feature of TIMEs and other members of this family is their ability to mobilize genomic DNA for transposition as part of composite transposons. These elements significantly influence the structure and properties of plasmids and other mobile genetic elements (MGEs). They may contain and move by transposition (i) plasmid replication systems, (ii) toxin-antitoxin systems and (iii) site-specific recombination modules that can resolve plasmid multimers. Some Tn 3 family elements may also transfer large segments of chromosomal DNA into plasmids, which increases the pool of mobile DNA that can take part in horizontal gene transfer.