Reassembly of flagellar B (alpha beta) tubulin into singlet microtubules: consequences for cytoplasmic microtubule structure and assembly.
B(alpha beta) tubulin was obtained from a homogeneous class of microtubules, the incomplete B subfiber of sea urchin sperm flagellar doublet microtubules, by thermal fractionation. The thermally derived soluble B tubulin fraction (100, 000 g-h) repolymerizes in vitro, yielding microtubule-like structures. The microtubule-associated protein (MAP) composition and certain assembly parameters of thermally derived B tubulin are different from those reported for sonication-derived flageller tubulin and purified vertebrate tubulin. The "microtubules" reassembled from thermally prepared B tubulin are composed of 12-15 protofilaments (73% possess 14 protofilaments). A certain number possess a single "adlumenal component" applied to their inside walls, regardless of the number of protofilaments. Following the first cycle of polymerization, 81% of the B tubulin and essentially 100% of the MAPs remain cold insoluble. Evidence suggests that B tubulin assembles faithfully into a B lattice, creating a j seam between two protofilaments that are laterally bonded in a A-lattice configuration. The significance of these seams is discussed in relation to the mechanism of microtubule assembly, the stability of observed ribbons of protofilaments, and the three-dimensional organization of microtubule-associated components.
D000818:Animals; D002474:Cell-Free System; D005407:Flagella / Q000648:ultrastructure*; D007700:Kinetics; D008297:Male; D008854:Microscopy, Electron; D008869:Microtubule-Associated Proteins; D008870:Microtubules / Q000648:ultrastructure*; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism; D012617:Sea Urchins; D012995:Solubility; D013696:Temperature; D014404:Tubulin / Q000378:metabolism*
D008869:Microtubule-Associated Proteins; D011506:Proteins; D014404:Tubulin