Kinetics of branch migration in double-stranded DNA.

Abstract

The branch migration rate in double-stranded DNA was measured using a unique substrate formed by the EcoRI restriction endonuclease [from Escherichia coli] on the dimeric figure-8 configuration of the phage G-4 replicative form DNA. The figure-8 and the X-form derived from it contain a junction of the kind postulated to occur in the Holliday structure and to be an essential feature of a number of recombination models. In the X-form this junction can branch migrate to an irreversible terminal configuration consisting of 2 linear monomers. The disappearance of X-forms was measured by EM. A treatment of branch migration as a random walk process was developed to permit the rate determination of the intrinsic process, a step movement of the junction by a distance of 1 base pair. A value of about 6 kbase pairs/s at 37.degree. C was obtained.