The Tc1/mariner Family of Transposable Elements

This chapter describes the family of Tc1/ mariner elements, their mechanism of transposition, and the regulation of transposition. It also talks about a few applications of this family of transposable element in forward and reverse genetics. The transposase proteins contain the typical DDE or DDD motif found in most transposases and integrases. Excision of P elements in Drosophila melanogaster has been used as a trigger to initiate introduction of new sequences into the original P element-containing site; it has been shown also for Tc1 that an ectopic transgenic template (marked by polymorphisms) can be used by the repair process. For several members of the Tc1/mariner transposase family a smaller truncated version of the transposase was seen. Possibly it is the way of reconstructing Sleeping Beauty transposase that is responsible for generating a protein that is more active than any element found in nature, where it is not in the best interest of the parasite transposable element to encode a transposase that is too active and might kill the host. The Tc1 as well as the Tc3 elements were studied for their target choice in vivo. Most mariner-type elements are known only from their sequences obtained through homology-based PCR screens or by sequence analysis (genomic or expressed sequence tag). There are two reasons to think that Tc1/mariner-type transposons may be good vectors for transgenesis: they have spread by horizontal transfer between species and are thus probably not host restricted, and they require only the transposase protein for complete transposition.