We report here an ATP-dependent formation and contraction, or syneresis, of a microtubule gel using microtubule proteins prepared from calf brains. Gel contraction is typically observable 15-30 min after ATP addition to microtubules assembled to steady state, and is complete after approximately 60 min, at which time the gel volume is reduced by as much as 75%. In contracted gels, microtubule bundles and aster-like structures are observable. Gelation-contraction requires only microtubule proteins present after purification by three cycles of assembly and disassembly.

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