Novel regulation of mitotic exit by the Cdc42 effectors Gic1 and Gic2

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• The Cdc42 signaling pathway is crucial for regulating cell division.
• Mitotic exit in yeast involves a complex network of proteins, including kinases and GTPases.
• Understanding these pathways is key to comprehending cell cycle control.

Purpose of the Study:

• To identify novel components of the yeast mitotic exit pathway.
• To elucidate the role of Cdc42 effectors Gic1 and Gic2 in mitotic exit.
• To investigate the mechanism by which Gic proteins regulate this process.

Main Methods:

• Genetic screening to identify pathway components.
• Analysis of gene deletions and mutations (e.g., cdc5-10, Deltalte1, Deltagic1, Deltagic2).
• Biochemical assays to study protein interactions (e.g., Gic1 binding to Bub2).

Main Results:

• Gic1 and Gic2 were identified as factors promoting mitotic exit independently of Ste20.
• Gic1's function requires Cdc42 activation and release from the bud cortex.
• Gic proteins are essential for mitotic exit when Cdc5 polo kinase and Lte1 are impaired.
• Gic1 directly binds Bub2, preventing Tem1 binding and thus interfering with Bfa1-Bub2 GTPase-activating protein function.

Conclusions:

• Cdc42-regulated Gic proteins are novel regulators of yeast mitotic exit.
• Gic proteins trigger mitotic exit by inhibiting the Bfa1-Bub2 complex.
• This pathway provides a crucial backup mechanism for cell cycle progression when primary regulators are compromised.