Abstract
In Escherichia coli, chi is a recombination hotspot that stimulates RecBCD-dependent exchange at and to one side of itself. chi activity is highest at chi and decreases with distance from chi . The decrease in chi activity may be a simple property of the physical distance over which chi can stimulate recombination. Alternatively, the decay in chi activity with distance may reflect the high likelihood that chi -stimulated recombination occurs in a single chi -proximal act, to the exclusion of additional chi -stimulated exchanges more distal to chi . To test the models, we determined if chi activity decreases as a function of physical distance (i.e., DNA base pairs) or genetic distance (homologous DNA base pairs). Our results indicate that chi activity decays as a function of genetic distance. In addition, we found that the sbcB gene product (exonuclease I, a 3' arrow right 5' ssDNA exonuclease) modulates the distance over which chi can act. In contrast, the recJ gene product (a 5' arrow right 3' ssDNA exonuclease) does not alter the decay of chi activity.
