FIG. 2.

Model for recombination mediated by the viral SynExo. Linear dsDNA, such as that produced during rolling circle replication by the virus or by the action of the packaging endonuclease on the packaging site, serves as the substrate. The exonuclease is shown resecting the 5′ end while the synaptase binds the resulting 3′-terminated ssDNA. The synaptasome mediates the search for homology promoting ssDNA annealing (SSA) with complementary ssDNA and strand invasion (SI) with homologous dsDNA. SI occurs with and without assistance from the host RecA protein (12, 39, 43). SI is proposed to occur by the synaptase alone in regions of ssDNA (produced, for example, during replication) (10).