Figure 8.
An excess of dsDNA alleviates the inhibition of DNA strand exchange in trans caused by ssDNA. RecA nucleoprotein filaments were incubated with a competitor ssDNA (#21; 12 μm) that had a high affinity for the secondary DNA-binding site. DNA strand exchange in trans was initiated by addition of mutually homologous dsDNA (#5 and #6) and 32P-labeled ssDNA (#5). Three different concentrations of these substrates were used: 12 μm of ssDNA and 24 μm dsDNA (1× dsDNA); 12 μm of ssDNA and 240 μm dsDNA (10× dsDNA); or 120 μm ssDNA and 24 μm of dsDNA (10× ssDNA). The product yield was normalized relative to the DNA substrate present at the lowest concentration in the reaction.