Table 3.

Effect of Salt Treatment on Kinesin Processivity

			Run length
Construct	Added salt	n	Observed	Corrected	Velocity
			μm	μm	μm/s
Wild type	250 mM KCl	43	0.30 ± 0.05	0.31 ± 0.05	0.42 ± 0.03
H1Q	250 mM KCl	54	0.50 ± 0.06	0.55 ± 0.07	0.42 ± 0.01
Wild type	120 mM KAc	75	1.1 ± 0.1	1.4 ± 0.2	0.416 ± 0.008
H1Q	120 mM KAc	69	1.7 ± 0.2	2.6 ± 0.5	0.465 ± 0.008

Single molecule measurements were made as described in the Materials and Methods and in Table . n is the number of events that were scored for each mutant. The run lengths after addition of KCl differed at P < 10⁻¹⁶ from those without added salt. The addition of K-acetate did not produce a significant change in the wild-type run length, but did for H1Q (P = 2 × 10⁻³). Salts were added to a buffer of 12 mM Pipes, pH 6.8, 1 mM EGTA, and 2 mM MgCl₂. The buffer pH was readjusted to 6.8 after the addition of potassium acetate (KAc).