Replicative transposition

Replicative transposition is a particular transposition event that is used by transposable bacterial viruses to replicate their genome. The key enzyme responsible for replicative transposition is a DDE-recombinase .

The best studied transposable bacterial virus is bacteriophage Mu.
During replicative transposition, interactions between DDE-recombinase A (MuA) four core subunits, the DNA ends and the enhancer (IAS) form the stable synaptic complex (SSC) .
The target DNA activator protein B (MuB) brings the target DNA to the transposition complex. DDE-recombinase A associated with MuB mediates single-strand nicks at the 3' ends of the integrated viral genome followed by strand transfer of the 3'-OH cleaved ends to the 5' ends of the cleaved cellular target DNA .
The flaps DNA are not resected by DDE-recombinase A and the resulting branched strand transfer joint is resolved by target-primed replication, which is initiated by the host PriA primosome and completed by host Pol III holoenzyme, resulting in two copies of the viral genome .
Host ClpX plays an essential transpososome-remodeling role by releasing the block between transposition and DNA replication. Successive rounds of replicative transposition can lead up to 100 copies of the viral genome.
Depending on the way the phage DNA nicked 3'-OH ends attack the target, the segment between the integrated viral genome and the target will be either deleted with excision of a chromosomal segment and one Mu DNA copy (binding to the same strand) or inverted (binding to the opposite strand, shown here). In case transposition targets a distinct DNA replicon, a plasmid for instance, the donor and target replicons will be fused by means of two copies of Mu in the same orientation (replicon fusion)