Activation of Chi, a recombinator, by the action of an endonuclease at a distant site

Chi is an Escherichia coli recombinator specific to the recBC pathway. In phage lambda, its activity is dependent on its orientation with respect to the orientation of the chromosome packaging origin, cos [Kobayashi, I., Murialdo, H., Crasemann, J.M., Stahl, M. M. & Stahl, F. W. (1982) Proc. Natl. Acad. Sci. USA 79, 5981-5985]. Chi in an inactive state is activated by the in vivo action of a restriction endonuclease at a distant site. This result supports a model for Chi activation in which a recombination machine enters a DNA duplex at an end and travels until it encounters a Chi properly oriented with respect to the direction of enzyme movement. Events are then initiated that lead to exchange in the neighborhood of Chi.