title: Analysis of Bub3 spindle checkpoint function in Xenopus egg extracts.
abstract: The spindle checkpoint delays the onset of anaphase if there are any defects in the interactions between spindle microtubules and kinetochores. This checkpoint has been reconstituted in vitro in Xenopus egg extracts, and here we use antibodies to Xenopus Bub3 (XBub3) to show that this protein is required for both the activation and the maintenance of a spindle checkpoint arrest in egg extracts. We detect two forms of XBub3 in egg extracts and find both to be complexed with the XBub1 and XBubR1 kinases. Only one form of XBub3 is apparent in Xenopus tissue culture (XTC) cells, and localisation studies reveal that, unlike the Mad proteins, which are concentrated at the nuclear periphery, XBub3 is diffusely localised throughout the nucleus during interphase. During early prophase it is recruited to kinetochores, where it remains until chromosomes align at the metaphase plate. We discuss the mechanism by which our alpha-XBub3 antibodies interfere with the checkpoint and possible roles for XBub3 in the spindle checkpoint pathway.
authors.affiliation: Wellcome Trust Centre for Cell Biology, Institute of Cell and Molecular Biology, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh, Scotland, EH9 3JR, UK. Kevin.Hardwick@ed.ac.uk
authors.forename: Leigh
authors.initials: L
authors.lastname: Campbell
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Hardwick
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000302:isolation & purification*; D002457:Cell Extracts; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D005057:Eukaryotic Cells / Q000378:metabolism*; D005260:Female; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D018386:Kinetochores / Q000378:metabolism; D046911:Macromolecular Substances; D008938:Mitosis / Q000502:physiology*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D009865:Oocytes; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D008941:Spindle Apparatus / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins
chemical_list: D000906:Antibodies; C489446:Bub3 protein, Xenopus; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D018076:DNA, Complementary; D005656:Fungal Proteins; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D020033:Protein Isoforms; D029867:Xenopus Proteins; D011494:Protein Kinases; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases