Figure 2.

BIR-dependent formation of LEU2 recombinants. (A) EcoRI-digested plasmid pWYL37 has homology only at one end to sites in the yeast genome. (B) The “LEU” segment at one end of the DSB may initiate new DNA synthesis, but the completion of the event requires that the newly synthesized DNA is displaced from the template and must rejoin to the other end of the DSB by a nonhomologous end-joining event. (C) A <1-kb “LEU” DNA fragment was transformed into the same strain shown in A. This fragment has no ARS sequence and cannot replicate autonomously. (D) Hit-and-run transformants containing a circular derivative of chromosome III sequences were recovered. A putative origin of replication, designated ARS-x, is apparently responsible for the ability of these all-yeast circles to replicate.