RecBCD bound to a blunt-ended DNA hairpin using data collected on ESRF beamlines ID14-1 and ID14-4. The structure was solved in the absence of ATP and so represents an initiation complex prior to translocation

The RecBCD enzyme binds at the broken DNA end and rapidly unwinds the duplex in an ATP-dependent manner. As unwinding proceeds, the 3’ terminated strand is continuously degraded by an endonuclease activity. This unwinding and digestion continues until the Chi sequence is encountered, at which point the enzyme pauses, and the nuclease switches to the other DNA strand. The enzyme then continues unwinding the duplex, digesting the 5’ terminated strand and loading the RecA strand-exchange protein onto the 3’ strand, now capped by the Chi sequence (Figure 76) in preparation for the next stage of HR.