FIG 1 .

Models of oligonucleotide recombination. (A) Single-strand annealing model of oligonucleotide recombination at DNA replication fork. The oligonucleotide is bound by the recombinase and annealed to complementary ssDNA arising at the replication fork. Larger gaps on the lagging strand because of discontinuous synthesis promote recombination with the lagging-strand oligonucleotide and give rise to the lag-lead bias. (B) Model of strand invasion. The oligonucleotide is bound by the recombinase, which locates homologous dsDNA and opens the DNA duplex, annealing the oligonucleotide to its complement and displacing the DNA that is identical in sequence, forming a D-loop.