DNASE-I INCREASES THE RATE-CONSTANT OF DEPOLYMERIZATION AT THE POINTED (-) END OF ACTIN FILAMENT

We show here that DNase is distinguished from other known actin-bindin g proteins by its unique ability to increase the depolymerization rate constant of actin at the pointed filament end, thereby speeding up de polymerization of filaments capped at their barbed ends. This action r equires relatively high DNase concentrations, 3 orders of magnitude hi gher than those needed to block elongation, although 10 times lower th an those needed for DNase binding to the side of the filament. We prop ose that at high DNase concentrations, steric interference between the two DNase molecules, bound to the ends of both strands of the two-sta rt actin helix, destabilizes actin binding to the filament.