Thus, p31comet, UbcH10, and Dynein work in concert during checkpoint inactivation.
DeAntoni et al. [25] proposed the "Template Model" explaining the mechanism of Mad2 recruitment to the kinetochore during checkpoint activation and subsequent transfer to sequester Cdc20.
The balance model is supported by the recent observation of residual activities of mitotic kinases during checkpoint arrest.
We used this assay to screen fission yeast mutants and thereby identify factors that act downstream of Ark1 during checkpoint silencing.
This phenotype is consistent with the human Mad2 phosphorylation studies [ 18] and suggests that Mph1 kinase activity could have inhibitory checkpoint signaling roles, perhaps disrupting Mad1-Mad2 kinetochore scaffolds during checkpoint silencing and/or interphase.
Consistent with a functional crosstalk between the Ddc2– Mec1 and 9 1 1 complexes during checkpoint signaling, there is a reported requirement for the 9 1 1 complex to stabilize Ddc2 foci in irradiated G1 cells (Barlow et al. 2008).
Ipl1 is also required for Mad2 association with kinetochores during checkpoint activation (Gillett et al. 2004), perhaps due to a requirement for Ipl1 in generating unattached kinetochores to which Mad1– Mad2 can be recruited (Pinsky et al. 2006).
The high affinity of the Bub1 Bub3 complex for MELTP sequences might explain why Bub1 is quite stably bound to kinetochores during checkpoint activation, as shown by fluorescence recovery after photobleaching (FRAP) experiments (Howell et al., 2004; Shah et al., 2004).
We propose that phosphorylation of Mad2 by Mph1 kinase is one of several posttranslational modifications of the MCC (Mad2-Mad3-Cdc20Slp1) thet stabilize the MCC-APC/C interaction and thereby inhibit APC/C activity during checkpoint arrest.
A theoretical evaluation was reported by Doncic and collaborators, who came to the conclusion that if the spindle assembly checkpoint worked through Cdc20 sequestration it would be more robust to concentration fluctuations that may occur during checkpoint activity as opposed to a spindle assembly checkpoint that operated through Cdc20 degradation (Doncic et al, 2006).
