Members of the Tc1/mariner superfamily of transposons isolated from fish appear to be transpositionally inactive due to the accumulation of mutations. Molecular phylogenetic data were used to construct a synthetic transposon, Sleeping Beauty, which could be identical or equivalent to an ancient element that dispersed in fish genomes in part by horizontal transmission between species. A consensus sequence of a transposase gene of the salmonid subfamily of elements was engineered by eliminating the inactivating mutations. Sleeping Beauty transposase binds to the inverted repeats of salmonid transposons in a substrate-specific manner, and it mediates precise cut-and- paste transposition in fish as well as in mouse and human cells. Sleeping Beauty is an active DNA-transposon system from vertebrates for genetic transformation and insertional mutagenesis.
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We have observed transposition of synthetic salmonid transposons in fish, mouse, and human cells. In addition, transposition of genetically marked transposons in a plasmid-to-plasmid transposition assay was significantly enhanced in microinjected zebrafish embryos in the presence of transposase (data not shown). Moreover, precision of the cut-and-paste reaction was remarkably maintained in heterologous cells; we have not encountered a single junction sequence that did not contain the predicted ends of the element and TA target site duplications flanking the insertion. Consequently, SB apparently does not need any obvious species-specific factor that would restrict its activity (i.e., efficiency and fidelity) to its original host. This observation is supported by the wide species-distribution and apparent success of the Tc1/mariner superfamily in the animal kingdom. Interestingly, the most significant enhancement, about 20-fold, of transposition was observed in human cells. Possible explanations of this phenomenon might be the absence of repressor-like factors and/or presence of stimulatory factors in human cells.