Fig. 2. Regulation of in vitro MT assembly by the Op18(1-57)-NR-helix. The upper panel shows elongation velocity at plus ends for MTs assembled at pH 7.5 with 11 µM tubulin alone or 11 µM tubulin plus the indicated concentrations of Op18(1-57)-NR-helix or Op18(25-57)-NR-helix. Catastrophe frequency at MT plus ends in the same experiment is shown in the lower panel. Data represent means±s.d. The number of events analyzed for elongation velocity and catastrophe rates, respectively, were Co, n=37 and 34; Op18(1-57)-NR-Helix 30 µM, n=14 and 30; 60 µM, n=23 and 25; Op18(25-57)-NR-helix 60 µM, n=35 and 50.