Generation of GTP-bound Ran by RCC1 is required for chromatin-induced mitotic spindle formation.
Chromosomes are segregated by two antiparallel arrays of microtubules arranged to form the spindle apparatus. During cell division, the nucleation of cytosolic microtubules is prevented and spindle microtubules nucleate from centrosomes (in mitotic animal cells) or around chromosomes (in plants and some meiotic cells). The molecular mechanism by which chromosomes induce local microtubule nucleation in the absence of centrosomes is unknown, but it can be studied by adding chromatin beads to Xenopus egg extracts. The beads nucleate microtubules that eventually reorganize into a bipolar spindle. RCC1, the guanine-nucleotide-exchange factor for the GTPase protein Ran, is a component of chromatin. Using the chromatin bead assay, we show here that the activity of chromosome-associated RCC1 protein is required for spindle formation. Ran itself, when in the GTP-bound state (Ran-GTP), induces microtubule nucleation and spindle-like structures in M-phase extract. We propose that RCC1 generates a high local concentration of Ran-GTP around chromatin which in turn induces the local nucleation of microtubules.
Carazo-Salas
R E
RE
EMBL, Heidelberg, Germany.
Guarguaglini
G
G
Gruss
O J
OJ
Segref
A
A
Karsenti
E
E
Mattaj
I W
IW
D000818:Animals; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D002843:Chromatin / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology*; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D008870:Microtubules / Q000502:physiology; D008938:Mitosis / Q000502:physiology*; D008954:Models, Biological; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011994:Recombinant Proteins; D012568:Schizosaccharomyces; D015398:Signal Transduction; D008941:Spindle Apparatus / Q000502:physiology*; D029867:Xenopus Proteins; D014982:Xenopus laevis; D020931:ran GTP-Binding Protein
D018797:Cell Cycle Proteins; D002457:Cell Extracts; D002843:Chromatin; D004268:DNA-Binding Proteins; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; C499304:RCC1 protein, Xenopus; C062521:RCC1 protein, human; D011994:Recombinant Proteins; D029867:Xenopus Proteins; D006160:Guanosine Triphosphate; D020931:ran GTP-Binding Protein