Three-step model for condensin activation during mitotic chromosome condensation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Chromosomes undergo significant structural changes during mitosis, involving chromatin compaction into mitotic chromosomes.
• The condensin complex, a multi-subunit ATPase, is crucial for establishing chromosome architecture and condensation.
• Fundamental questions remain regarding how condensin promotes condensation and how cell cycle machinery regulates its activity.

Purpose of the Study:

• To review the role of post-translational modifications, specifically multi-site phosphorylation, in regulating condensin activity during the cell cycle.
• To propose a model for condensin regulation based on phosphorylation patterns.

Main Methods:

• Analysis of phosphorylation sites identified through proteome-wide mass spectrometry.
• Examination of evolutionary conservation of condensin phosphorylation landscapes.
• Identification of kinases regulating condensin activity in vivo.

Main Results:

• Condensin phosphorylation patterns are highly conserved across evolution.
• Multiple kinases regulate condensin activity in vivo.
• A conserved phosphorylation landscape suggests a coordinated regulatory mechanism.

Conclusions:

• The ultrasensitive/kinase switch model proposes that multi-site phosphorylation of condensin allows for maintained or increased chromosome condensation under fluctuating cyclin-CDK activity.
• This model explains how chromosome condensation is sensitive to CDK activity in early mitosis and becomes insensitive in late mitosis.