Motor protein decoration of microtubules grown in high salt conditions reveals the presence of mixed lattices

We have used back-projection methods to obtain three-dimensional maps of mo tor-protein decorated nine and ten protofilament microtubules polymerized i n the presence of high salt and preserved in vitreous ice. The resulting th ree-dimensional maps show that the vast majority of these microtubules have multiple seams, rather than being helical as would be expected according t o the lattice accommodation model. These results indicate that microtubules should be analyzed by back-projection before using helical reconstruction approaches, and that nine and ten protofilament microtubules polymerized in high salt conditions are not suitable for helical analysis. (C) 1999 Acade mic Press.