KINE 1000 Lecture 7: Increase production of CKI
4 Jun 2018
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Inrease prodution of CKI, dk inhiitor
proteins
- CKI called Sic1, binds to & inactivates M-cdk in late Mitosis & G1
- Sic1 is inhibited by M-cdk, which phosphorylates Sic1 during mitosis &
thereby promotes its ubiquitylation by SCF.
- Decline in M-cdk activity that occurs in late mitosis causes Sic1 protein to
accumulate. This CKI helps keep M-cdk activity low after mitosis
o Decrease transcription of M-cyclins inactivated M-cdks in late mitosis
- In activation of M-cdk by cdh1 & Sic1 leads to decreases M-cyclin gene
transcription & thus decreases M-cyclin synthesis. Gene regulatory
proteins that promote expression of G1/S & S-cyclins are inhibited during
G1
• Cdh1-APC/C activation, CKI accumulation & decrease cyclin gene expression act
to ensure all cdk activity is suppressed
• To escape stable G1 state to initiate new cycle, G1/S cdk activity rises in late G1
Summary
• Mitosis complete formation of pair of daughter nuclei
• Cytokinesis depends on ring of actin & myosin filaments that contracts in late mitosis
• Positioning of contractile ring is determines by signals
• Dephosphorylation of cdk targets which results from cdk inactivation in anaphase triggers
cytokinesis after anaphase
• After cytokinesis, cell enters stable G1 state of low cdk activity where it waits for signal to
enter new cell cycle
Control of Cell Division & Cell Growth
• Cell number depends on amount of cell division & cell death
• Organ & body size is determined by 3 processes: cell growth & cell division & cell
survival
- Both regulated by intracellular & extracellular signal molecules
• Extracellular signal molecules that regulate cell growth & division are soluable
secreted proteins bound to surface of cells
• Three Major Classes of Extracellular Signal molecules
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