Fig. 1.

Chromosomal construct used to measure deletion formation through recombination between identical or diverged repeats. Two nonfunctional lacZ genes are cloned in close proximity (0.5 kb) on the E. coli chromosome. The first lacZ gene contains a C-terminal deletion (lacZ′ΔC), whereas the second contains an N-terminal deletion (′lacZΔN). The two gene fragments share an overlapping region of 1.3 kb (filled boxes) that is 100% identical or 4% diverged at the DNA sequence level. Nonoverlapping lacZ gene C-terminal and N-terminal regions are presented as hatched boxes. A single recombination event between two gene fragments reconstitutes a functional lacZ gene and deletes the intervening region. plac, lactose promoter; lacZ, gene coding for β-galactosidase; lacY, gene coding for lactose permease; yfp, gene coding for yellow fluorescent protein.