Insertion site preference of Mu, Tn5, and Tn7 transposons

Three transposons, Mu, Tn5, and Tn7, were used to generate insertions in the same set of fosmids containing Candida glabrata genomic DNA. Tn7 demonstrates markedly less insertion bias than either Mu or Tn5, with both Mu and Tn5 biased toward sequences containing guanosine (G) and cytidine (C). This preference of Mu and Tn5 yields less uniform spacing of insertions than for Tn7, in the adenosine (A) and thymidine (T) rich genome of C. glabrata (39% GC).In light of its more uniform distribution of insertions, Tn7 should be considered for applications in which insertion bias is deleterious.Transposons, mobile DNA elements that can integrate into target DNA molecules, are useful for insertional mutagenesis, gene tagging, gene transfer, and sequencing applications. A major class of transposable elements used for genome engineering is DNA 'cut and paste' transposons. The transposases for DNA transposons cut the transposon away from the donor DNA by a variety of mechanisms and the excised transposon integrates into a new target site by joining of its 3'OH termini to staggered positions on the top and bottom DNA strands of the target. This staggered joining results in a target site duplication of a defined number of base pairs, which can be used to map precisely the site of integration for the transposon [1].In most of the applications of transposons to molecular biology, it is important that the transposon insert into target DNA with little to no sequence bias. Limited sequence bias will lead to more complete coverage of a region for a given number of insertion events. However, most transposons have been shown to exhibit some preference for certain sequences or sequence features [1]. Clearly, insertion site bias may be a confounding factor for large scale transposon mutagenesis projects.A number of manuscripts reporting insertion motifs for various transposons have been published, but the target DNA, transposition protocol and environment (in vitro versus in vivo) vary wid