Budding yeast complete DNA synthesis after chromosome segregation begins

Area of Science:

• Cell Biology
• Genetics
• Molecular Biology

Background:

• Faithful genetic information transmission requires complete genome replication before cell division.
• Genome replication and chromosome segregation are traditionally thought to be temporally separated events in mitosis.

Purpose of the Study:

• To investigate the temporal relationship between DNA replication and chromosome segregation in unperturbed yeast cells.
• To determine if DNA synthesis can occur concurrently with later stages of mitosis.

Main Methods:

• Microscopy and DNA staining techniques were used to observe DNA synthesis.
• Analysis of cyclin-dependent kinase (Cdk) activity during mitosis.
• Mutation rate analysis in subtelomeric regions.

Main Results:

• DNA synthesis was observed to continue during anaphase (late mitosis) in 20-40% of yeast cells.
• Decreased cyclin-Cdk activity during mitotic exit permits the completion of DNA synthesis in challenging genomic regions.
• Late mitotic DNA synthesis correlates with increased mutation rates and copy number variations in subtelomeric regions.

Conclusions:

• Yeast cells exhibit temporal overlap between DNA synthesis and chromosome segregation during normal growth.
• This overlap may optimize population-level growth rate and promote genetic exploration.
• The findings challenge the strict separation model of replication and segregation.