Three-dimensional structure of the Tn5 synaptic complex transposition intermediate

Genomic evolution has been profoundly influenced by DNA transposition, a pr ocess whereby defined DNA segments move freely about the genome. Transposit ion is mediated by transposases, and similar events are catalyzed by retrov iral integrases such as human immunodeficiency virus-1 (HIV-1) integrase, U nderstanding how these proteins interact with DNA is central to understandi ng the molecular basis of transposition. We report the three-dimensional st ructure of prokaryotic Tn5 transposase complexed with Tn5 transposon end DN A determined to 2.3 angstrom resolution. The molecular assembly is dimeric, where each double-stranded DNA molecule is bound by both protein subunits, orienting the transposon ends into the active sites. This structure provid es a molecular framework for understanding many aspects of transposition, i ncluding the binding of transposon end DNA by one subunit and cleavage by a second, cleavage of two strands of DNA by a single active site via a hairp in intermediate, and strand transfer into target DNA.