Related Experiment Video
Updated: Oct 16, 2025
12:26
Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
Published on: May 3, 2018
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G1 cyclin-Cdk promotes cell cycle entry through localized phosphorylation of RNA polymerase II
Mardo Kõivomägi1, Matthew P Swaffer1, Jonathan J Turner1
1Department of Biology, Stanford University, Stanford, CA 94305, USA.
Science (New York, N.Y.)
|October 14, 2021
Summary
Budding yeast cell division is triggered by Cln3-Cdk1, which phosphorylates RNA polymerase II, not Whi5. This promotes transcription at key promoters, linking cell cycle and transcriptional regulation.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Cell division initiation involves cyclin-dependent kinases (Cdks) inactivating transcriptional inhibitors.
- In budding yeast, the G1 cyclin Cln3-Cdk1 complex was thought to phosphorylate Whi5, releasing SBF and committing cells to division.
Purpose of the Study:
- To investigate the precise mechanism by which Cln3-Cdk1 initiates cell division in budding yeast.
- To clarify the role of Whi5 phosphorylation in cell cycle commitment.
- To explore the link between cell cycle progression and transcriptional regulation.
Main Methods:
- Biochemical assays to test Whi5 as a substrate for Cln3-Cdk1.
- Phosphorylation site analysis of RNA polymerase II subunit Rpb1.
- Genetic experiments involving synthetic recruitment of kinases to promoters.
Main Results:
- Whi5 was found to be a poor substrate for Cln3-Cdk1.
- Cln3-Cdk1 directly phosphorylates the S5 position of Rpb1's C-terminal heptapeptide repeats.
- Cln3-Cdk1 binds to SBF-regulated promoters, and its function can be mimicked by Ccl1-Kin28 when targeted to SBF.
Conclusions:
- Cln3-Cdk1 initiates cell division by phosphorylating Rpb1 at SBF-regulated promoters, thereby promoting transcription.
- This mechanism blurs the distinction between cell cycle and transcriptional Cdks.
- The findings highlight an ancient relationship between cell cycle control and transcriptional processes.
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