Figure 7.
ssDNA with a high-affinity for the secondary site inhibits DNA strand exchange in trans. (A) Time course of the DNA strand exchange in trans carried out in the presence of a low- or high-affinity ssDNA inhibitor. A standard reaction mixture was divided in two. Each was supplemented with competing ssDNA (120 μm) that had either high (#21) or low (htr#1) affinity for the secondary site of RecA protein. DNA strand exchange in trans was initiated by the addition of mutually homologous dsDNA (#5 and #6) and 32P-labeled ssDNA (#5) to both mixtures. (B) Concentration dependence of the inhibition of the reaction in trans by the same competitors. The indicated amounts of ssDNA were added to the reaction mixtures prior to addition of homologous ssDNA and dsDNA substrates. The reactions were carried out for 15 min.