Model of microhomology-mediated U-turn-like inversions. The red shape represents the DNA polymerase and the blue shape represents the DNA helicase. Yellow and green strands represent inverted microhomologies. Impediments to replication fork progression might force the leading strand polymerase to pause and eventually unload. In the presence of RecA, the impediment may be bypassed to restart replication accurately. In the absence of RecA and Whirly proteins, a microhomology located at the 3′ end of the nascent strand can anneal to its complementary inverted repeat on the opposite strand and restart the replication fork on the wrong strand. The dotted arrow represents a multistep process.
