title: Unstained microtubules studied by cryo-electron microscopy. Substructure, supertwist and disassembly.
abstract: Unstained microtubules embedded in amorphous ice have been studied by cryo-electron microscopy and image reconstruction. The structural integrity is well preserved, judging by the similarity of optical diffraction patterns with X-ray fiber diagrams. Protofilaments are not straight but show a variable right-handed twist around the tubule axis with a pitch of several micron. While rapid freezing of warm solutions (about 37 degrees C) leaves microtubules intact, gradual cooling, followed by rapid freezing, allows one to visualize the time-course of microtubule breakdown. Disassembly proceeds both from the ends and from inside, and short protofilament fragments are among the early breakdown products.
mesh_terms: D000818:Animals; D005615:Freezing; D008854:Microscopy, Electron; D008870:Microtubules / Q000648:ultrastructure*; D008968:Molecular Conformation; D013552:Swine; D014961:X-Ray Diffraction