For a strain that lacks all three functions of the checkpoints, we used rad3Δ, which lacks the central checkpoint kinase.
To investigate the importance of checkpoint-mediated transcription relative to the other two functions, we built strains that lack one or more functions but maintained the other functions of the checkpoints (Table 2).
These conclusions are consistent with previous work showing recovery from replicative stress is a critical function of the checkpoint [22], [23].
Since the main function of the checkpoint is to prevent chromosome missegregation events, deletion of any SAC protein is expected to affect the missegregation rate in a manner related to the specific role of this protein in the checkpoint.
Restoration of extended MBF-dependent transcription provides modest, but reproducible, resistance to HU in both rad3Δ and cds1Δ cells, comparable in degree to the resistance provided by the cell-cycle arrest function of the checkpoint.
In addition, it should be noted that this arrest defect affects not only the direct cell-cycle arrest function of the checkpoint, but also the indirect cell-cycle arrest function provided by checkpoint-dependent expression of mik1 [see below and 20], [21].
Assessing the function of the checkpoint in human cancer by analyzing mutation of genes or protein expression, however, would be impractical.
Among the components of the MCC, BubR1 plays two major roles in the functions of the mitotic checkpoint.
These findings argue against a strictly linear pathway, in which Mec1 acts through Rad53 to inhibit DDK, but rather suggest that there are Rad53-independent functions of the replication checkpoint in meiosis.
The predicted network reproduces many of the known features of the SAC and provides new insights about the function of this checkpoint.
