Structure/function insights into Tn5 transposition.

Abstract Prokaryotic transposon 5 (Tn 5 ) serves as a model system for studying the molecular mechanism of DNA transposition. Elucidation of the X-ray co-crystal structure of Tn 5 transposase complexed with a DNA recognition end sequence provided the first three-dimensional picture of an intermediate in a transposition/retroviral integration pathway. The many Tn 5 transposase–DNA co-crystal structures now available complement biochemical and genetic studies, allowing a comprehensive and detailed understanding of transposition mechanisms. Specifically, the structures reveal two different types of protein–DNA contacts: cis contacts, required for initial DNA recognition, and trans contacts, required for catalysis. Protein–protein contacts required for synapsis are also seen. Finally, the two divalent metals in the active site of the transposase support a ‘two-metal-ion’ mechanism for Tn 5 transposition.