Direct visualization of the formation and structure of RecA/dsDNA complexes.

A direct visualization of the construction of RecA/DNA nucleofilament complexes was obtained using high-resolution atomic force microscopy (AFM). It showed that the complex consisted of helical loops, with each helical loop composed of units of size equivalent to approximately six monomers. The contour of stretched DNA that was embedded beneath RecA monomers was also observed directly. Images of RecA/DNA complexes showed both left- and right-handed helices, with a range of helical pitches. This was considered to imply that the complexes were flexible enough such that they are prone to compression forces that occur during sample preparation.