Procedure

1.

Make rhodamine seeds by mixing 1 part rhodamine-tubulin + 4 parts PC-tubulin + MgCl2 to make final concentration of 4 mg/mL tubulin + 4 mM MgCl2 after glycerol and Mg·GTP are added. Centrifuge tubulin mixture at 155,000g at 2°C for 5 min in a Beckman TLA ultracentrifuge prior to adding glycerol and Mg·GTP. Withdraw supernatant and add 1.5 mM Mg·GTP + 20% (v/v) glycerol. Incubate 3.5 min at 37°C in 2.5 microliter volume to make rhodamine seeds.

2.

Withdraw 1.5 microliters of rhodamine seeds into 4.5 microliters of tubulin mix pre-warmed 1 min at 37°C to make asymmetrically labeled fluorescent microtubules with a bright rhodamine seed at the minus end. Tubulin mix is 1 part NEM-tubulin + 1 part PC tubulin (4 mg/mL total tubulin concentration) + 2.8 mM Mg·GTP. Incubate 5 min at 37°C. Then add 19 microliters PM + 40 microliters taxol at 37°C.

3.	Add asymmetrically labeled fluorescent microtubules and antifade to motility assay mixes. Observe under fluorescence using a SIT camera or cooled CCD camera. Record motility on Super VHS tape.