FIG. 10.

Tripartite recombination. (A) A plasmid with a gapped copy of leu2 is gap repaired from two chromosomal templates. Genetic information must be recovered from two different chromosomes and assembled into the plasmid to create a complete LEU2 gene. (B) Two models to explain the production of a LEU2 gene. DNA synthesis can be initiated independently from both 3′ ends of the broken plasmid (top). Both newly synthesized strands are then unwound from the template and annealed. Alternatively, DNA synthesis can be initiated from one 3′ end, and template switching ensures the recovery of all the required LEU2 sequences (bottom). Then the newly synthesized strand anneals with the other 3′ end. In both cases, DNA synthesis is conservative: the newly synthesized DNA is unwound from its template.