A direct role of Mad1 in the spindle assembly checkpoint beyond Mad2 kinetochore recruitment.
The spindle assembly checkpoint (SAC) ensures accurate chromosome segregation by delaying entry into anaphase until all sister chromatids have become bi-oriented. A key component of the SAC is the Mad2 protein, which can adopt either an inactive open (O-Mad2) or active closed (C-Mad2) conformation. The conversion of O-Mad2 into C-Mad2 at unattached kinetochores is thought to be a key step in activating the SAC. The "template model" proposes that this is achieved by the recruitment of soluble O-Mad2 to C-Mad2 bound at kinetochores through its interaction with Mad1. Whether Mad1 has additional roles in the SAC beyond recruitment of C-Mad2 to kinetochores has not yet been addressed. Here, we show that Mad1 is required for mitotic arrest even when C-Mad2 is artificially recruited to kinetochores, indicating that it has indeed an additional function in promoting the checkpoint. The C-terminal globular domain of Mad1 and conserved residues in this region are required for this unexpected function of Mad1.
The Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
Thomas
T
Kruse
Marie Sofie Yoo
MS
Larsen
Garry G
GG
Sedgwick
Jón Otti
JO
Sigurdsson
Werner
W
Streicher
Jesper V
JV
Olsen
Jakob
J
Nilsson
D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D018386:Kinetochores / Q000378:metabolism*; D059566:M Phase Cell Cycle Checkpoints; D064246:Mad2 Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary
D018797:Cell Cycle Proteins; C501384:MAD1L1 protein, human; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D009687:Nuclear Proteins