RecA polymerization on double-stranded DNA by using single-molecule manipulation: The role of ATP hydrolysis

The polymerization of RecA on individual double-stranded DNA molecules is s tudied. A linear DNA (lambda DNA 48.5 Kb), anchored at one end to a cover g lass and at the other end to an optically trapped 3-mu m diameter polystyre ne bead, serves as a template. The elongation caused by RecA assembly is me asured in the presence of ATP and ATP[gamma S]. By using force extension an d hydrodynamic recoil, a value of the persistence length of the RecA-DNA co mplex is obtained. In the presence of ATP, the polymer length is unstable, first growing to saturation and then decreasing. This suggests a transient dynamics of association and dissociation for RecA oh a double-stranded DNA, the process being controlled by ATP hydrolysis. Part of this dynamics is s uppressed in the presence of ATP[gamma S], leading to a stabilized RecA-DNA complex. A one-dimensional nucleation and growth model is presented that m ay account for the protein assembly.