Kinetic mechanism of end-to-end annealing of actin filaments

We investigated the effect of actin filament length and capping protein on the rate of end-to-end annealing of actin filaments. Long filaments were fr agmented by shearing and allowed to recover. Stabilizing filaments with pha lloidin in most experiments eliminated any contribution of subunit dissocia tion and association to the redistribution of lengths but did not affect th e results. Two different assays, fluorescence microscopy to measure filamen t lengths and polymerization to measure concentration of barbed filament en ds, gave the same time-course of annealing. The rate of annealing declines with time as the average filament length increases. Longer filaments also a nneal slower than short filaments. The second-order annealing rate constant is inversely proportional to mean polymer length with a value of 1.1 nM(-1 ) s(-1)/length in subunits. Capping protein slows but does not prevent anne aling. Annealing is a highly favorable reaction with a strong influence on the length of polymers produced by spontaneous polymerization and should be considered in thinking about polymer dynamics in cells. (C) 2001 Academic Press.