Spindle Checkpoint Requires Mad1-bound and Mad1-free Mad2
AUTOR(ES)
Chung, Eunah
FONTE
The American Society for Cell Biology
RESUMO
The spindle checkpoint prevents anaphase from occurring until all chromosomes have attached properly to the mitotic spindle. The checkpoint components Mad1 and Mad2 associate with unattached kinetochores and are probably involved in triggering the checkpoint. We now demonstrate that in Xenopus egg extracts Mad1 and Mad2 form a stable complex, whereas a fraction of Mad2 molecules is not bound to Mad1. The checkpoint establishment and maintenance are lost upon titrating out free Mad2 with an excess of Mad1 or a truncated Mad1 (amino acids 326–718, Mad1C) that contains the Mad2-binding region. Mad1N (amino acids 1–445) that binds kinetochores, but not Mad2, reduces Mad1 and Mad2 at kinetochores and abolishes checkpoint maintenance. Furthermore, the association between Mad2 and Cdc20, the activator for the anaphase-promoting complex, is enhanced under checkpoint-active condition compared with that at metaphase. Immunodepletion analysis shows that the Mad1-free Mad2 protein is unable to bind Cdc20, consistent with the model that kinetochore localization of Mad2 facilitates the formation of Mad2–Cdc20 complex. This study demonstrates that the ratio between Mad1 and Mad2 is critical for maintaining a pool of Mad1-free Mad2 that is necessary for the spindle checkpoint. We propose that Mad2 may become activated and dissociated from Mad1 at kinetochores and is replenished by the pool of Mad1-free Mad2.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=111122Documentos Relacionados
- Mad2 binding to Mad1 and Cdc20, rather than oligomerization, is required for the spindle checkpoint
- The Spindle Checkpoint of Budding Yeast Depends on a Tight Complex between the Mad1 and Mad2 Proteins
- Specific association of estrogen receptor β with the cell cycle spindle assembly checkpoint protein, MAD2
- HAT cofactor Trrap regulates the mitotic checkpoint by modulation of Mad1 and Mad2 expression
- Conformation-specific binding of p31comet antagonizes the function of Mad2 in the spindle checkpoint