Figure 1.

Model for phage λ Red recombination. (A) Overview of the activities of λ Exo and Redβ in the single-strand annealing pathway. (B) Domain structure of Redβ. The functions of each domain are listed. Residues 178–194 of Redβ likely form a flexible linker that connects the two domains. (C) Model of the complex, based on the α₃β₃ hexamer observed in the crystal, which did not include the Redβ N-terminal domains. The C-terminal domains of each Redβ monomer each bind to the λ Exo trimer, leaving the N-terminal domains free to bind the nascent 3′-overhang. According to the model, as the λ Exo trimer moves along the DNA from right to left, it loads Redβ monomers onto the nascent 3′-overhang, one after another.