Ultrastructural localization of the high molecular weight proteins associated with in vitro-assembled brain microtubules

This is the publisher's version, also available electronically from http://jcb.rupress.org/content/65/1/237.Microtubules isolated from brain extracts by in vitro assembly (1, 19, 23) are composed principally of two tubulins and two high molecular weight proteins (microtubule-associated proteins [MAPS] 1 and 2) (2,5,7,20). Recently, it was demonstrated that in vitro-assembled brain microtubules (neurotubules) are coated with filaments (5, 7) which are similar to the filaments attached to neurotubules in situ (4, 15, 21, 24, 25), and it was suggested that the filaments are composed of the higher molecular weight MAPs (5, 7, 12). In this study, microtubules were assembled in the presence and absence of the MAPs, and thin sections of the microtubules were examined by electron microscopy. The results show that the filaments only occur on microtubules assembled in the presence of the MAPs and it is therefore concluded that the filaments are composed of the high molecular weight MAP's

Ultrastructural localization of the high molecular weight proteins associated with in vitro-assembled brain microtubules

This is the publisher's version, also available electronically from http://jcb.rupress.org/content/65/1/237.Microtubules isolated from brain extracts by in vitro assembly (1, 19, 23) are composed principally of two tubulins and two high molecular weight proteins (microtubule-associated proteins [MAPS] 1 and 2) (2,5,7,20). Recently, it was demonstrated that in vitro-assembled brain microtubules (neurotubules) are coated with filaments (5, 7) which are similar to the filaments attached to neurotubules in situ (4, 15, 21, 24, 25), and it was suggested that the filaments are composed of the higher molecular weight MAPs (5, 7, 12). In this study, microtubules were assembled in the presence and absence of the MAPs, and thin sections of the microtubules were examined by electron microscopy. The results show that the filaments only occur on microtubules assembled in the presence of the MAPs and it is therefore concluded that the filaments are composed of the high molecular weight MAP's

Directionality of brain microtubule assembly in vitro

Chicks were injected intra-cerebrally with [(3)H]leucine, and (3)H-labeled microtubules were assembled in vitro in the brain supernatants. Pieces of these (3)H-labeled microtubules were then incubated with unlabeled brain tubulin subunits under conditions where the subunits assembled onto the labeled pieces. Electron microscopic autoradiography of the negatively-stained microtubules showed all of the radioactivity at one end of the tubules as they increased in length. This clearly demonstrated that the microtubules of brain in this in vitro system were being assembled unidirectionally