Murray Weingarten

A heat stable protein essentail for microtubule assembly has been isolated. This protein, which we designate tau (tau), is present in association with tubulin purified from porcine brain by repeated cycles of polymerization. Tau is separated from tubulin by ion exchange chromatography on phosphocellulose. In the absence of tau, tubulin exists entirely as a 6S dimer of two polypeptide chains (alpha and beta tubulin) with a molecular weight of 120,000, which will not assemble into microtubules in vitro. Addition of tau completely restores tubule-forming capacity. Under nonpolymerizing conditions, tau converts 6S dimers to 36S rings-structures which have been implicated as intermediates in tubule formation. Hence, tau appears to act on the 6S tubulin dimer, activating it for polymerization. The unique ability of tau to restore the normal features of in vitro microtubule assembly makes it likely that tau is a major regulator of microtubule formation in cells.

Tubulin purified by phosphocellulose chromatography and free of accessory proteins will not form microtubules in the absence or presence of microtubule initiating sites (flagellar microtubules). The capacity for growth onto pre-existing "seeds" can be restored by the addition of small quantities of partially purified tau protein. Larger quantities restore the capacity for spontaneous assembly. These results suggest that tubulin requires tau for both initiation and growth of microtubules and that tau is incorporated into the microtubule throughout its length.

Depolymerization products of purified microtubules from porcine brain were examined by sedimentation analysis and electron microscopy. The complete depolymerization mixture exhibited 36S and 6S components in concentration-dependent equilibrium, whether depolymerization was caused by low temperature or by calcium ion. These components were recognized by electron microscopy as spirals and rings, and small particles. Agarose column chromatography yielded two major fractions, a leading one comprising mostly 36S and some 6S material and a trailing one of solely 6S material. The latter had high specific colchicine-binding activity and no tendency to polymerize. For the leading peak material these properties were the converse. It is proposed that tubulin molecules (of mass 110,000 daltons) exist in two states, here called X and Y, with those of the X-state equivalent to the material found predominantly in the trailing fraction, and those of the Y-state equated with the material in the leading fraction. Participation of tubulin molecules in microtubule assembly and disassembly is discussed, based on the assumption that those of both states have longitudinal and lateral binding domains whose strengths differentially depend upon temperature and calcium-ion concentration.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProperties of the depolymerization products of microtubules from mammalian brainMurray D. Weingarten, Mary M. Suter, Dan R. Littman, and Marc W. KirschnerCite this: Biochemistry 1974, 13, 27, 5529–5537Publication Date (Print):December 1, 1974Publication History Published online1 May 2002Published inissue 1 December 1974https://pubs.acs.org/doi/10.1021/bi00724a012https://doi.org/10.1021/bi00724a012research-articleACS PublicationsRequest reuse permissionsArticle Views155Altmetric-Citations106LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts