Promotion of microtubule assembly by neurofilament-associated microtubule-associated proteins.
Intact neurofilaments (NF) purified from mammalian brain and spinal cord promote the assembly of microtubules in solutions of pure phosphocellulose (PC)-purified tubulin. This assembly is temperature-dependent and is inhibited by mitotic spindle inhibitors. The ability of NF to induce microtubule formation is 20% of that of purified microtubule-associated proteins (MAPs), whereas MAPs comprise less than 5% of the protein in the NF preparations. The inducing activity of NF is rapidly lost on boiling. When intact NF are incubated with PC-tubulin and then centrifuged, tubulin is sedimented together with the filaments. This association is inhibited by colchicine and podophyllotoxin and is cold-sensitive. NF purified to homogeneity under denaturing conditions and then reassembled completely lack the ability to promote the assembly of PC-tubulin or to bind tubulin on a centrifugation assay. No MAPs are present in these preparations, though these filaments have the ability to bind exogenous MAPs. While these experiments do not rule out an intrinsic microtubule-assembly-promoting activity, they suggest that this activity is due to nontriplet proteins in the preparation, most likely filament-associated MAPs.
D000818:Animals; D001921:Brain / Q000648:ultrastructure; D002417:Cattle; D003078:Colchicine / Q000494:pharmacology; D003599:Cytoskeleton / Q000502:physiology*; D006358:Hot Temperature; D008854:Microscopy, Electron; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D008870:Microtubules / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D011817:Rabbits; D013116:Spinal Cord / Q000648:ultrastructure
D008869:Microtubule-Associated Proteins; D003078:Colchicine