Microtubule nucleation by gamma-tubulin-containing rings in the centrosome.
The microtubule cytoskeleton of animal cells does not assemble spontaneously, but instead requires the centrosome. This organelle consists of a pair of centrioles surrounded by a complex collection of proteins known as the pericentriolar material (PCM). The PCM is required for microtubule nucleation. The minus, or slow-growing, ends of microtubules are embedded in the PCM and the plus, or fast-growing, ends project outwards into the cytoplasm during interphase, or into the spindle apparatus during mitosis. gamma-Tubulin is the only component of the PCM that is so far implicated in microtubule nucleation. Here we use immuno-electron microscopic tomography to show that gamma-tubulin is localized in ring structures in the PCM of purified centrosomes without microtubules. When these centrosomes are used to nucleate microtubule growth, gamma-tubulin is localized at the minus ends of the microtubules. We conclude that microtubule-nucleating sites within the PCM are ring-shaped templates that contain multiple copies of gamma-tubulin.
Department of Biochemistry & Biophysics, University of California at San Francisco 94143-0448, USA.
M
M
Moritz
M B
MB
Braunfeld
J W
JW
Sedat
B
B
Alberts
D A
DA
Agard
D000818:Animals; D018385:Centrosome / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure*; D004330:Drosophila; D007150:Immunohistochemistry; D016253:Microscopy, Immunoelectron; D008870:Microtubules / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D014404:Tubulin / Q000032:analysis* / Q000502:physiology*
D014404:Tubulin