Direct visualization of the formation of RecA/dsDNA complexes at the single-molecule level

The assembly of RecA on linear dsDNA with ATPγS in the reaction was elucidated using atomic force microscopy (AFM) on a single-molecule level. It was found that assembly generally (∼95%) proceeded from a single nucleation site that started from one end of the DNA strand. About 5% of the complexes were formed starting either from both ends or from the middle of dsDNA strand. In all these cases, the RecA coating was contiguous for each region suggesting the binding of RecA to DNA is cooperative. The AFM observation provides direct experimental evidence to show how RecA binds to linear dsDNA in the presence of ATPγS.