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Fission yeast genes involved in coupling mitosis to completion of DNA replication
Abstract:
We have isolated fission yeast mutants that enter mitosis when DNA replication is blocked with hydroxyurea. The mutants define eight linkage groups, three of which consist of alleles of the rad1, rad3, and rad17 genes. Recently, these fission yeast genes have been shown to be required for radiation-induced cell cycle arrest, as is the budding yeast RAD9 gene. The other five genes are called hus (hydroxyurea sensitive) 1-5. We propose that these genes participate in an intracellular signal transduction pathway that monitors the completion of DNA replication and transmits information to the mitotic control protein cdc2. Mutations that bypass the requirement for cdc25 (an activator of the mitotic regulator cdc2) also uncouple mitosis from DNA replication. However, mitosis is blocked by inhibitors of DNA replication in strains in which the cdc25 gene has been deleted, indicating that although cdc25 influences the coupling of mitosis to the completion of DNA replication, it is not essential for this control.
Insights
Fission yeast mutants were identified that enter mitosis despite blocked DNA replication. These mutants reveal genes involved in monitoring DNA replication and signaling to cell division control, crucial for cell cycle regulation.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Cell cycle progression requires coordination between DNA replication and mitosis.
- Hydroxyurea (HU) is a chemical agent that inhibits DNA replication.
- Fission yeast mutants can bypass normal cell cycle checkpoints.
Purpose of the Study:
- To identify fission yeast genes that regulate the coupling of DNA replication to mitosis.
- To investigate the role of DNA replication checkpoints in preventing premature entry into mitosis.
Main Methods:
- Isolation and genetic analysis of fission yeast mutants sensitive to hydroxyurea.
- Characterization of mutations affecting cell cycle progression during DNA replication inhibition.
- Genetic analysis of known cell cycle control genes, including rad and cdc genes.
Main Results:
- Eight linkage groups of hydroxyurea-sensitive (hus) mutants were identified.
- Three mutants contained alleles of previously identified radiation-sensitive genes (rad1, rad3, rad17).
- Mutations bypassing cdc25 allowed mitosis during DNA replication block, but cdc25 deletion did not fully uncouple mitosis from replication.
Conclusions:
- The identified genes (hus1-5, rad1, rad3, rad17) likely form a signal transduction pathway monitoring DNA replication.
- This pathway transmits information to the cdc2-mediated mitotic control.
- cdc25 plays a role in, but is not essential for, coupling mitosis to DNA replication completion.