Figure 6.

Model for λ Red recombination incorporating the action of Rap protein. The model depends on the observation that Rap is involved in Red pathway recombination at a double-strand break (T. Tarkowski and F. W. Stahl, personal communication). Step i, a double-strand break in λ DNA is a substrate for the Redα exonuclease. Redα (triangle) degrades the double-strand end to generate a 3′ tail. Step ii, this single-strand tail is paired with a homologous chromosome by either Redβ or RecA proteins (spheres). Step iii, the annealed 3′ end can prime DNA replication and protein-free sections of the D-loop are a substrate for Rap cleavage. Step iv, trimming of the DNA followed by ligation results in a splice product. See Discussion and Introduction for further details and references.