Development of hyperactive sleeping beauty transposon vectors by mutational analysis.

The Sleeping Beauty (SB) transposable element is a promising vector for transgenesis in vertebrates and is being developed as a novel, nonviral system for gene therapeutic purposes. A mutagenesis approach was undertaken to improve various aspects of the transposon, including safety and overall efficiency of gene transfer in human cells. Deletional analysis of transposon sequences within first-generation SB vectors showed that the inverted repeats of the element are necessary and sufficient to mediate high-efficiency transposition. We constructed a "sandwich" transposon, in which the DNA to be mobilized is flanked by two complete SB elements arranged in an inverted orientation. The sandwich element has superior ability to transpose >10-kb transgenes, thereby extending the cloning capacity of SB-based vectors. We derived hyperactive versions of the SB transposase by single-amino-acid substitutions. These mutations act synergistically and result in an almost fourfold enhancement of activity compared to the wild-type transposase. When combined with hyperactive transposons and transiently overexpressed HMGB1, a cellular cofactor of SB transposition, hyperactive transposases elevate transposition by almost an order of magnitude compared to the first-generation transposon system. The improved vector system should prove useful for efficient gene transfer in vertebrates.