Fcp1-dependent dephosphorylation is required for M-phase-promoting factor inactivation at mitosis exit

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Mitosis progression in eukaryotes depends on the precise regulation of cyclin B-dependent kinase 1 (cdk1), also known as the M-phase-promoting factor (MPF).
• MPF activity is sustained by feedback loops preventing inhibitory cdk1 phosphorylation and cyclin B degradation until mitotic spindle assembly.
• The role of specific phosphatases in reversing these feedback loops for MPF inactivation and anaphase onset remains unclear.

Purpose of the Study:

• To investigate whether specific phosphatases are required for MPF inactivation and the subsequent exit from mitosis.
• To elucidate the role of Fcp1, an RNA polymerase II C-terminal domain phosphatase, in the regulation of MPF activity.

Main Methods:

• Biochemical assays to assess phosphatase activity and target interactions.
• Genetic studies in eukaryotes to evaluate the in vivo function of Fcp1.
• Identification of Fcp1 targets involved in mitotic regulation.

Main Results:

• Timely inactivation of MPF requires the activity of Fcp1 in a transcription-independent manner.
• Fcp1 directly targets Cdc20, USP44, and Wee1, key regulators of anaphase onset and MPF activity.
• These findings highlight Fcp1's critical role in coordinating dephosphorylation and ubiquitination events during mitosis exit.

Conclusions:

• Fcp1 is essential for the timely inactivation of MPF, a crucial step for exiting mitosis.
• Fcp1 acts as a critical link between dephosphorylation and ubiquitination pathways, regulating key mitotic proteins.
• This study reveals a novel function for Fcp1 in cell cycle control beyond its known role in transcription.