title: Bub3 interaction with Mad2, Mad3 and Cdc20 is mediated by WD40 repeats and does not require intact kinetochores.
abstract: The kinetochore checkpoint pathway, involving the Mad1, Mad2, Mad3, Bub1, Bub3 and Mps1 proteins, prevents anaphase entry and mitotic exit by inhibiting the anaphase promoting complex activator Cdc20 in response to monopolar attachment of sister kinetochores to spindle fibres. We show here that Cdc20, which had previously been shown to interact physically with Mad2 and Mad3, associates also with Bub3 and association is up-regulated upon checkpoint activation. Moreover, co-fractionation experiments suggest that Mad2, Mad3 and Bub3 may be concomitantly present in protein complexes with Cdc20. Formation of the Bub3-Cdc20 complex requires all kinetochore checkpoint proteins but, surprisingly, not intact kinetochores. Conversely, point mutations altering the conserved WD40 motifs of Bub3, which might be involved in the formation of a beta-propeller fold devoted to protein-protein interactions, disrupt its association with Mad2, Mad3 and Cdc20, as well as proper checkpoint response. We suggest that Bub3 could serve as a platform for interactions between kinetochore checkpoint proteins, and its association with Mad2, Mad3 and Cdc20 might be instrumental for checkpoint activation.
authors.affiliation: Dipartimento di Biotecnologie e Bioscienze, Piazza della Scienza 2, 20126 Milano, Italy.
authors.forename: R
authors.initials: R
authors.lastname: Fraschini
authors.forename: A
authors.initials: A
authors.lastname: Beretta
authors.forename: L
authors.initials: L
authors.lastname: Sironi
authors.forename: A
authors.initials: A
authors.lastname: Musacchio
authors.forename: G
authors.initials: G
authors.lastname: Lucchini
authors.forename: S
authors.initials: S
authors.lastname: Piatti
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D002352:Carrier Proteins; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D002850:Chromatography, Gel; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018386:Kinetochores / Q000378:metabolism*; D064246:Mad2 Proteins; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010957:Plasmids / Q000378:metabolism; D017354:Point Mutation; D011233:Precipitin Tests; D011485:Protein Binding; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D020449:Repetitive Sequences, Amino Acid; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
chemical_list: C070352:BUB3 protein, S cerevisiae; C577495:CDC20 protein, S cerevisiae; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; C577695:MAD2 protein, S cerevisiae; D064246:Mad2 Proteins; D009687:Nuclear Proteins; D011506:Proteins; D029701:Saccharomyces cerevisiae Proteins