The cell membrane of the unicellular algae Distigma proteus is associated with arrays of parallel microtubules. Fragments of the membrane-microtubule complex have been isolated and partially purified. The microtubules were stable in vitro at room temperature as well as at 0 degree C, but were specifically and rapidly disassembled by Ca2+. After removal of all endogenous microtubules, the membrane-microtubule complex could be reassembled from brain microtubule protein and denuded Distigma membrane fragments. The readded microtubules bound in a fixed orientation, and only to those regions of membrane that are normally associated with microtubules in vivo.

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