A comparative study of the in vitro polymerization of tubulin in the presence of the microtubule-associated proteins MAP2 and tau.
At concentrations of microtubule-associated proteins MAP2 and tau inducing maximal microtubule formation, MAP2 promotes higher rates and higher levels of microtubule nucleation that tau. Microtubules polymerized to steady state by tau show a 2-fold higher rate of tubulin loss compared to microtubules polymerized by MAP2. Microtubules polymerized in the presence of both MAP2 and tau contain lower levels of MAP2 (0.06 mol/mol of tubulin) and tau (0.07 mol/mol of tubulin) than microtubules polymerized in the exclusive presence of MAP2 (0.2 mol/mol of tubulin) or tau (0.25 mol/mol of tubulin). Addition of tau to microtubules polymerized by MAP2 results in incorporation of tau into microtubules (0.047 mol/mol of tubulin) and loss of MAP2 (0.1 mol/mol of tubulin). Similarly, incubation of microtubules polymerized by tau in the presence of MAP2 results in microtubule incorporation of MAP2 (0.1 mol/mol of tubulin) and loss of tau (0.08 mol/mol of tubulin). Microtubules and their ribbon precursor contain comparable levels of MAP2. Cross-sectional views of microtubules show no difference in the number of protofilaments (13 to 15) forming the MAP2 and tau microtubules. Fingerprints of cysteine-labeled tryptic peptides of two tau polypeptides (tau 4 and tau 6) are very similar and differ totally from similar fingerprints of MAP2.
D000818:Animals; D001921:Brain / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008869:Microtubule-Associated Proteins; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D012234:Rho Factor / Q000378:metabolism*; D013552:Swine; D014157:Transcription Factors / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism*
D046911:Macromolecular Substances; D008869:Microtubule-Associated Proteins; D009419:Nerve Tissue Proteins; D011506:Proteins; D012234:Rho Factor; D014157:Transcription Factors; D014404:Tubulin