Fig. 9. GDP enhances minus-end-directed motility of early endocytic vesicles. Fluorescent-polarity-marked microtubules were prepared as described (Murray et al., 2000). MT-bound vesicles were incubated for 5 minutes with buffer alone or with buffer containing 4 mM GDP, following which 50 µM ATP was added to produce vesicle motility. The bars indicate the percentage of vesicles that moved upon ATP addition in the minus-end or plus-end directions. For each experiment, the number of motile vesicles in either direction versus the total number of motile vesicles that were examined is in parentheses. *P<0.01.