Figure 3.

Free ssDNA is not produced as an intermediate of inverse DNA strand exchange. The dsDNA substrate (30 ng in oligonucleotide 2) was treated with 1 munit of P1 nuclease either in the presence or absence of RecA protein (as indicated) for 60 min at 37°C (lanes 2,3,4). (Lanes 1,5) Negative controls in which the P1 nuclease was omitted. (Lane 2) The positive control demonstrating degradation of the ssDNA; in this lane, oligonucleotide 2 was mixed with noncomplementary φX174 ssDNA, instead of the complementary M13 ssDNA.