Recombination

Genetic recombination in bacteria is a nonreciprocal process whereby segments of genetic material from two different sources are brought together into a single DNA molecule. Site-specific recombination involves the recombination of two DNA molecules at specific locations variously called insertion sequences (IS), long terminal repeats (LTRs), and attachment sites (att). The integration of the bacteriophage λ into the E. coli chromosome is a common example of site-specific recombination involving att (Figure 7-2). Both possess att sites, which are recognized by the λ integration and excision enzymes. Both chromosomes share a short region of homology indicated by "O." This region of homology is flanked by short DNA sequences that are unique to the organism. The flanking E. coli regions are indicated by B and B', while those of the λ phage are indicated by P and P'. After integration of the phage DNA into that of E. coli by site specific recombination, the λ chromosome is flanked by the sequences BOP' and POB'.