Measuring Homologous Recombination Rates between Chromosomal Locations in Salmonella

Homologous recombination between two similar DNA molecules, plays an important role in the repair of double-stranded DNA breaks. Recombination can occur between two sister chromosomes, or between two locations of similar sequence identity within the same chromosome. The assay described here is designed to measure the rate of homologous recombination between two locations with sequence similarity within the same bacterial chromosome. For this purpose, a selectable/counter-selectable genetic cassette is inserted into one of the locations and homologous recombination repair rates are measured as a function of recombinational removal of the inserted cassette. This recombinational repair process is called gene conversion, non-reciprocal recombination. We used this method to measure the recombination rates between genes within gene families and to study the stability of mobile genetic elements inserted into members of gene families.