Homologous pairing in genetic recombination. The pairing reaction catalyzed by Escherichia coli recA protein.

Purified recA protein, which is essential for genetic recombination of Escherichia coli, catalyzed ATP-dependent homologous pairing of double-stranded DNA and single-stranded fragments to form D-loops. When the double-stranded DNA was nicked circular DNA (form II) or linear DNA (form III), the reaction proceeded nearly linearly during 30 min of incubation at 37 degrees C. When the double-stranded DNA was superhelical (form I), anomalous kinetics was observed.