Practice question

Resected 3' single-stranded overhangs are rapidly coated by RPA, which must be replaced by recombinase to become invasive. In bacteria RecA, and in eukaryotes Rad51 and meiosis-specific Dmc1, polymerize directionally on ssDNA into right-handed helical nucleoprotein filaments with ATP. This filament stretches DNA and performs homology search via base-triplet sampling, then catalyzes pairing and strand exchange with intact duplex donor. Invasion creates a displacement loop and provides 3'-OH primer for repair synthesis, establishing heteroduplex DNA without requiring ATP hydrolysis for pairing itself.