Chi sites function to
Chi, or crossover hotspot instigator, is an octamer sequence that regulates recombination frequency along bacterial chromosome. In Escherichia coli, RecBCD complex translocates as powerful helicase-nuclease degrading DNA until encountering Chi in proper orientation. RecC subunit recognizes 5'-GCTGGTGG-3' and triggers allosteric conformational switch attenuating 3'→5' nuclease while upregulating 5'→3' activity producing 3' overhang and actively loading RecA onto that strand. This conversion switches RecBCD from destructive exonuclease into recombination-promoting enzyme, causing stimulation of
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: RecBCD and Chi-Mediated Recombination Regulation
