FIGURE 6.

Comparing the salt sensitivity of Sc-MyoII, Sc-MyoV, and skeletal muscle myosin-II motility rates with yeast actins. The average actin filament gliding rates generated by Sc-MyoII (A), Sc-MyoV (B), and muscle myosin-II (C) are compared using three different yeast actins (wild-type, D24A-D25A, and E99A-E100A) at two final salt concentrations (50 and 150 mm KCl). For positive readings, the number of filaments measured (n) were as follows: Sc-MyoII: n = 54–64, except the 50 mm KCl D24A-D25A (n = 6) and 150 mm KCl E99A-E100A (n = 27) values, which were limited by decreased motility efficiency; Sc-MyoV: n = 60; muscle myosin-II: n = 60, except the 150 mm KCl wild-type actin (n = 12) value, which was limited by decreased motility efficiency. Measurements with wild-type yeast actin were generated in parallel with those for D24A-D25A and E99A-E100A mutant actins (i.e. independently of the measurements performed earlier in Figs. 3C and 4C). A uniform concentration of actin filaments (25 nm) was applied to motility chambers throughout. For each myosin, average motility rates (± S.E.) are presented relative to the value measured for wild-type yeast actin at 50 mm KCl (which is set to 1).