The group of C. Dekker (Delft University) directly probed the interactions involved in homology search by combining magnetic and optical tweezers. They have found that homology search and recognition requires opening of the helix and can therefore be accelerated by unwinding the DNA. This is exactly the energy barrier predicted by the conformational proofreading model. The data indicate a physical picture for homology recognition in which the fidelity of the search process is governed by the distance between the DNA-binding sites. The authors conclude that their interpretation of the measurements "is akin to a conformational proofreading scheme ... where the dsDNA, and not the RecA filament, is the active, recognizing search entity. A large conformational mismatch exists between the target-bound and unbound states of the dsDNA. The target-bound state is accessed via energetically unfavorable intermediate states, as discussed above. The conformational mismatch improves the selectivity of the recognition reaction." In other words, they identified the energetic barrier and have shown that indeed the double-stranded DNA is the active participant, since it has to pass this barrier.