Coating DNA with RecA Protein to Distinguish DNA Path by Electron Microscopy

To understand, at the molecular level, the mechanism of enzymes that act on DNA, it is highly informative to know the topology of their substrates and products. To describe fully the topology of a DNA knot or catenane, it is necessary to know the overpassing and underpassing segments when two DNA helices cross. Conventional microscopy rarely allows such resolution. Coating DNA with RecA protein (1 ,2 ) allows the unambiguous determination of a DNA crossover (3 -5 ).