Cdc18p can block mitosis by two independent mechanisms

Area of Science:

• Cell Cycle Regulation
• Genomic Stability
• Molecular Biology

Background:

• The DNA replication checkpoint is crucial for maintaining genomic integrity by preventing premature mitosis.
• In Schizosaccharomyces pombe, this checkpoint involves the phosphorylation of cdc2p to inhibit mitosis.
• The cdc18 gene plays a vital role in initiating S phase and establishing the DNA replication checkpoint.

Purpose of the Study:

• To investigate the distinct roles of the N-terminal and C-terminal domains of the cdc18 protein in cell cycle control.
• To elucidate the mechanisms by which cdc18p regulates the DNA replication checkpoint and mitosis.
• To determine the relationship between cdc18p domains and known checkpoint and kinase components.

Main Methods:

• Functional analysis of cdc18p N-terminal and C-terminal domains.
• Investigating the genetic interactions between cdc18p and DNA replication checkpoint genes (rad1, rad3, rad9, rad17, hus1, cut5).
• Assessing the requirement of wee1p/mik1p tyrosine kinases for cdc18p-mediated mitotic inhibition.
• In vivo association studies between cdc18p and cdc2p/cdc13p.

Main Results:

• The C-terminus of cdc18p initiates DNA replication and mediates checkpoint function, acting upstream of checkpoint genes and requiring wee1p/mik1p.
• The N-terminus of cdc18p also inhibits mitosis but functions independently of the DNA replication checkpoint genes and wee1p/mik1p.
• The N-terminus of cdc18p directly binds to the cdc2p/cdc13p mitotic kinase in vivo.

Conclusions:

• The cdc18 protein possesses distinct functional domains that differentially regulate the cell cycle.
• The C-terminal domain integrates with the canonical DNA replication checkpoint pathway.
• The N-terminal domain bypasses normal checkpoint controls by directly interacting with the mitotic kinase, potentially representing an unphysiological mechanism.