Figure 1.
Rad51-promoted strand exchange between circular ssDNA and homologous linear dsDNA. (A) DNA substrates, joint molecule, and completely strand-exchanged product (nicked circular dsDNA). ss, circular ssDNA; ds, linear dsDNA; jm, joint molecules; nc, nicked circular dsDNA. (B and C) Kinetics of strand exchange. After preincubation of 32P-labeled pBluescript SK(+) circular ssDNA with Rad51 and RPA, the reaction was started by the addition of homologous linear dsDNA with either 3′ or 5′ complementary overhanging ends prepared by cleavage of the pBluescript SK(+) DNA with either ApaI or EcoRI restriction endonuclease. At the indicated times, samples (6 μl) were removed, and the DNA products were analyzed by agarose gel electrophoresis followed by autoradiography (B); quantitation of these data are shown in C. Joint molecules formed by linear dsDNA with 3′ (○) or 5′ (•) overhanging ends; nicked circular dsDNA formed by linear dsDNA with 3′ (□) or 5′ (■) overhanging ends.