Fizzy is required for activation of the APC/cyclosome in Xenopus egg extracts.
The Xenopus homologue of Drosophila Fizzy and budding yeast CDC20 has been characterized. The encoded protein (X-FZY) is a component of a high molecular weight complex distinct from the APC/cyclosome. Antibodies directed against FZY were produced and shown to prevent calmodulin-dependent protein kinase II (CaMKII) from inducing the metaphase to anaphase transition of spindles assembled in vitro in Xenopus egg extracts, and this was associated with suppression of the degradation of mitotic cyclins. The same antibodies suppressed M phase-promoting factor (MPF)-dependent activation of the APC/cyclosome in interphase egg extracts, although they did not appear to alter the pattern or extent of MPF-dependent phosphorylation of APC/cyclosome subunits. As these phosphorylations are thought to be essential for APC/cyclosome activation in eggs and early embryos, we conclude that at least two events are required for MPF to activate the APC/cyclosome, allowing both chromatid segregation and full degradation of mitotic cyclins. The first one, which does not require FZY function, is the phosphorylation of APC/cyclosome subunits. The second one, that requires FZY function (even in the absence of MAD2 protein and when the spindle assembly checkpoint is not activated) is not yet understood at its molecular level.
Lorca
T
T
Centre de Recherches de Biochimie Macromoléculaire, CNRS UPR 1086, 1919 route de Mende, 34293 Montpellier Cedex 5, France.
Castro
A
A
Martinez
A M
AM
Vigneron
S
S
Morin
N
N
Sigrist
S
S
Lehner
C
C
Dorée
M
M
Labbé
J C
JC
D000595:Amino Acid Sequence; D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001483:Base Sequence; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary; D004789:Enzyme Activation; D005656:Fungal Proteins; D006801:Humans; D008025:Ligases / Q000378:metabolism*; D016200:Maturation-Promoting Factor / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010063:Ovum; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D043743:Ubiquitin-Protein Ligase Complexes; D044767:Ubiquitin-Protein Ligases; D014981:Xenopus; D029867:Xenopus Proteins
D000906:Antibodies; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D064199:Cdc20 Proteins; C577501:Cdc20 protein, Xenopus; D018797:Cell Cycle Proteins; D018076:DNA, Complementary; D005656:Fungal Proteins; D009687:Nuclear Proteins; D029867:Xenopus Proteins; C577488:CDC20 protein, human; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases; D016200:Maturation-Promoting Factor; D008025:Ligases