Figure 2.

Changes in DNA structure during single-strand annealing (SSA). Double-strand break (DSB) in DNA having homologous repeats flanking DSB (dark blue and orange boxes) is a substrate for SSA (A). A combined action of DNA helicases and nucleases results in 5′ ends resection and production of 3′ overhangs (B) that are annealed to juxtapose the repeats (C). Protruding 3′ single-stranded fragments are removed by endonucleolytic cleavage and remaining 3′ ends are extended by a DNA polymerase (arrows) to synthesize DNA fragments with the use of an intact template of complimentary strand (D). DNA ligase reseals, lacking phosphodiester bonds. Resulting DNA is shorter than the parental molecule by the distance between homologous repeats and the length of one repeat (E). Therefore, SSA is potentially mutagenic even in its normal functioning. The proteins involved in A-E are described in the main text. This figure does not correspond to actual proportions within DNA processed by SSA.