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G1-phase and B-type cyclins exclude the DNA-replication factor Mcm4 from the nucleus
K Labib1, J F Diffley, S E Kearsey
1ICRF Clare Hall Laboratories, South Mimms, Hertfordshire, EN6 3LD, UK.
Nature Cell Biology
|November 24, 1999
Summary
Cyclin-dependent kinases (CDKs) prevent DNA replication re-initiation by excluding Mcm4 from the nucleus in yeast. Both G1 and B-type cyclins contribute to this Mcm4 nuclear exclusion, impacting prereplicative complex assembly.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Cyclin-dependent kinases (CDKs) regulate the cell cycle, controlling DNA replication initiation and preventing re-replication.
- Prereplicative complexes (pre-RCs) are essential for DNA replication, and their assembly at origins must be tightly regulated.
- Mcm4 is a crucial component of the pre-RC, playing a vital role in DNA replication.
Purpose of the Study:
- To investigate the role of CDKs in regulating Mcm4 localization within the cell.
- To determine how different cyclin types (G1-phase and B-type) influence Mcm4 nuclear exclusion.
- To understand the mechanism by which CDKs prevent DNA replication re-initiation.
Main Methods:
- Budding yeast model system.
- Cell cycle analysis.
- Nuclear-cytoplasmic fractionation.
- Western blotting to detect Mcm4 levels.
Main Results:
- CDKs were shown to exclude the essential pre-RC component Mcm4 from the nucleus in budding yeast.
- Both G1-phase and B-type cyclins were found to induce Mcm4 nuclear exit.
- Origin firing, triggered by B-type cyclins, is preceded by Mcm4 nuclear exclusion.
Conclusions:
- CDK-mediated nuclear exclusion of Mcm4 is a key mechanism preventing DNA replication re-initiation within a single cell cycle.
- G1 cyclins may reduce the cell's capacity for pre-RC assembly prior to S-phase entry.
- These findings provide insights into the precise regulation of DNA replication.
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Cyclins and cyclin-dependent kinases (Cdks) are the primary cell cycle regulators and function at the cell...
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