Stable MCC binding to the APC/C is required for a functional spindle assembly checkpoint.

Area of Science:

• Cell biology
• Molecular biology
• Genetics

Background:

• The spindle assembly checkpoint (SAC) prevents premature anaphase onset until chromosomes align.
• Cdc20 is a key mitotic co-activator of the anaphase-promoting complex/cyclosome (APC/C).
• The mitotic checkpoint complex (MCC) inhibits Cdc20, but its stable association with APC/C for SAC function is debated.

Purpose of the Study:

• To investigate the role of conserved motifs (IR and C-Box) in Cdc20.
• To determine if MCC formation or MCC-APC/C binding is essential for SAC function.

Main Methods:

• Analysis of Cdc20 mutants lacking IR or C-Box motifs.
• Assessment of MCC assembly and binding to APC/C.
• Evaluation of SAC function in cells expressing Cdc20 mutants.

Main Results:

• Mutations in IR and C-Box motifs of Cdc20 did not prevent MCC assembly.
• IR motif integrity was critical for stable MCC binding to the APC/C.
• Cdc20 mutants with impaired IR motif binding resulted in a compromised SAC due to competition with uninhibited Cdc20.

Conclusions:

• Stable association of the MCC with the APC/C is essential for a functional spindle assembly checkpoint.
• The IR motif of Cdc20 plays a critical role in mediating this stable interaction.