Figure 21.

Red-promoted dsDNA recombineering via ssDNA intermediates. λ Exo binds to one end of a dsDNA substrate and degrades the 5′-ending strand. The long ssDNA generated by Exo is bound by Beta (exactly how and to what extent is not known). Beta then promotes annealing to ssDNA regions of the replication fork, much like the model in Fig. 20 for DNA oligos. The large nonhomologous ssDNA region encoding the drug^R marker (brown line) is presumably stabilized by Beta bound to regions flanking the nonhomology. When the next replication fork passes through, the gene replacement is completed. This model was originally proposed by Yu et al. (376), and corroborated by the studies of Mosberg et al. (378).