A Bub2p-dependent spindle checkpoint pathway regulates the Dbf2p kinase in budding yeast

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Mitotic exit in eukaryotes requires inactivation of mitotic kinases, primarily through cyclin degradation controlled by the anaphase-promoting complex (APC).
• The spindle checkpoint prevents premature mitotic exit by inhibiting APC when the spindle is abnormal or kinetochores are unattached.
• DBF2, a budding yeast gene, is implicated in preventing cyclin degradation and blocking mitotic exit when mutated, but its precise function is unknown.

Purpose of the Study:

• To elucidate the function of the DBF2 gene and its encoded protein kinase (Dbf2p) in the cell cycle.
• To investigate the role of the spindle checkpoint in regulating Dbf2p kinase activity.
• To identify the specific spindle checkpoint components that control Dbf2p.

Main Methods:

• Genetic analysis of DBF2 and spindle checkpoint mutants in budding yeast.
• Biochemical assays to measure Dbf2p kinase activity.
• Investigating interactions between Dbf2p, Bub2p, and Mps1p.

Main Results:

• Dbf2p kinase activity is directly targeted and controlled by the spindle checkpoint.
• Bub2p, a conserved spindle checkpoint protein, specifically inhibits Dbf2p activity.
• Bub2p functions in a parallel branch of the spindle checkpoint, independent of most other known checkpoint components.
• Mps1p initiates this Bub2p-mediated inhibition of Dbf2p.

Conclusions:

• Dbf2p kinase is a novel target of the spindle checkpoint, regulated by Bub2p.
• This pathway represents a distinct branch of the spindle checkpoint, initiated by Mps1p.
• Understanding this regulation is critical for comprehending accurate mitotic exit and cell cycle control.