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. 2002 Jun 4;99(12):7917–7921. doi: 10.1073/pnas.122218499

Figure 1.

Figure 1

Preincubation of Dr RecA protein with dsDNA leads to faster production of DNA strand exchange products. Reactions contained 2 μM Dr RecA protein, 6 μM circular ss M13mp8 DNA, 12 μM linear duplex M13mp8 DNA (PstI-cut), 0.6 μM Ec SSB, 2 mM ATP, and an ATP-regenerating system. Reactions in A–C were carried out at pH 7.5, whereas those in D were done at pH 8.1. In the DS → SS reactions, the Dr RecA protein was preincubated with the linear dsDNA with the ATP for 40 min. The ssDNA was then added to start the reaction, and the SSB was added 5 min later. In the SS → DS reactions, the Dr RecA protein was preincubated with the ssDNA for 5 min, followed by the addition of SSB and ATP, with the reaction initiated after another 5 min by addition of the linear dsDNA. The labels S, I, and P denote the linear duplex DNA, the joint molecule reaction intermediates, and the nicked circular products of DNA strand exchange, respectively. The reaction itself is illustrated in Fig. 4.