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

Abstract

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.

Structure and composition of the cytoskeleton of nucleated erythrocytes I. The presence of microtubule-associated protein 2 in the marginal band.

“…7), immunoelectrophoresis (30), and immunodiffusion (data not shown) . The results summarized above confirm the proposal that the cytoplasmic microtubules have associated with their surfaces one or more characteristic proteins called MAPs, a term coined previously by Sloboda et al (32) to refer to a class of high molecular weight proteins that are stoichiometrically associated with the tubulin subunit lattice of in vitro assembled vertebrate brain microtubules (10,19,24,30,33). The term MAP has since come to refer to a general class of proteins that associate with and appear to modulate some of the characteristics of in vitro assembled brain microtubules .…”

“…wall of the microtubule in a manner analogous to that previously described for brain microtubules (2,10,19,24) .…”

“…For thin sectioning, lysed cells in washed medium were fixed for 1 h in 2% glutaraldehyde in wash medium, post£ixed, embedded, and sectioned as previously described (10,30). All observations were made with a JEOL IOOCX electron microscope operated at 80 kV.…”

Identity and Origin of the ATPase activity associated with neuronal microtubules. I. The ATPase activity is associated with membrane vesicles.

“…In addition to tubulin these preparations also contain microtubule-associated proteins (MAPs) that bind to microtubules with high affmity, and correspond to hairlike projections on microtubule surfaces (8,22). These observations and the fact that neuronal cells exhibit microtubule-dependent motility in the form ofaxonal transport have led to much speculation that MAPs may function as microtubule crossbridges in the cell.…”

Scanning electron microscopy of cytoplasmic filaments in rat anterior pituitary cells.

“…Microtubule-associated proteins (MAPS) are known to form filamentous structures projecting from the surfaces of microtubules (DENTLER et al, 1975;MURPHY and BORISY, 1975). SUPRENANT and DENTLER (1982) demonstrated that MAPS can form connections between a pancreatic secretory granule and isolated brain microtubules.…”