G2M transition

The transition of cells from G2 to mitosis is dependent on the activity of the cylin/CDK complex, CDC2/cyclin B. Phosphorylation by CDC2 has been linked to several events required for mitosis entry, with targets including nuclear lamins and chromatin proteins. The activity of CDC2 is tightly regulated to ensure mitotic events do not begin until DNA replication is complete. Activation of CDC2 is a result of accumulation of cyclin B occurring as cells progress through S phase, peaking in late G2. Inactivation of CDC2 occurs by phosphorylation while dephosphorylation is associated with G2-M transition.

Delayed transition is commonly observed in G2-phase cells exposed to agents such as radiation and chemotherapy. The resulting G2 block is thought to allow time to repair DNA damage, while loss of this G2 checkpoint is often observed in cancerous cells.

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