Transposons are genetic elements that are capable of moving within and between genomes. They are mobilized by a transposon-encoded transposase protein that excises the transposon from its original DNA context and reintegrates it into a new genomic locus.

Phage Mu is the first DNA transposition system for which an in vitro transposition reaction was established. The original in vitro system and versions thereof have been instrumental in deciphering the mechanistic details of DNA transposition in general, and have formed a basis for the development of advanced Mu-based genetic tools. The minimal in vitro DNA transposition system of Mu is highly efficient and displays very low target site selectivity, ideal features for many applications.