Chi recombination activity in phage lambda decays as a function of genetic distance

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Chi sites are essential recombination hotspots in Escherichia coli.
• Chi stimulates RecBCD-dependent genetic exchange.
• Chi activity is highest at the site and diminishes with distance.

Purpose of the Study:

• To investigate the mechanism of chi activity decay with distance.
• To differentiate between physical and genetic distance models for chi activity.
• To determine the roles of sbcB and recJ gene products in chi activity modulation.

Main Methods:

• Experimental determination of chi activity decay.
• Analysis of chi activity as a function of physical DNA distance (base pairs).
• Analysis of chi activity as a function of genetic distance (homologous DNA base pairs).

Main Results:

• Chi activity was found to decay as a function of genetic distance, not physical distance.
• The sbcB gene product (exonuclease I) was identified as a modulator of the effective distance of chi action.
• The recJ gene product did not influence the decay of chi activity with distance.

Conclusions:

• Genetic distance, rather than physical distance, governs the decay of chi hotspot activity.
• Exonuclease I (sbcB) plays a role in defining the range of chi-mediated recombination.
• RecJ does not impact the distance-dependent decrease in chi activity.