Transpososome

Transpososome is a nucleoprotein complex that forms during the transposition of DNA elements. It consists of transposase enzymes bound to the ends of a transposon, often in cooperation with host factors and the target DNA, and serves to bring the transposon ends into synapsis so that excision and insertion can occur. In many systems the complex is referred to as the paired-end complex or transpososome.

Formation and composition: Transposase molecules bind to each transposon end and assemble into a higher-order complex, frequently as dimers or larger oligomers. The ends are held in close contact within the synaptic assembly, which positions catalytic sites for the cleavage of donor DNA and subsequent integration into a target site. Accessory proteins and host DNA-binding factors may influence assembly, stability, and target choice, and the exact architecture of the transpososome varies among transposon families.

Function and mechanism: The transpososome coordinates the two essential steps of cut-and-paste transposition: excision from the donor molecule and strand transfer into the recipient DNA. The catalytic activity is typically carried out by a transposase with a conserved catalytic motif, and the complex often facilitates the generation of target-site duplications upon insertion. The assembly is dynamic, with subunits exchanging as the reaction proceeds in some systems.

Diversity and significance: Transpososome architecture reflects the diversity of transposon families, from simple dimeric cores to more complex multimeric assemblies. The transpososome is central to transposition, contributing to genetic variation and genome evolution, and its function can impact genome stability. Structural and biochemical studies continue to elucidate its detailed organization across systems.