Budding Yeast Rif1 Controls Genome Integrity by Inhibiting rDNA Replication

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Rif1 protein acts as a negative regulator of DNA replication initiation in eukaryotes.
• The rDNA locus is a large, repetitive chromosomal region prone to replication challenges.

Purpose of the Study:

• To investigate the role of Rif1 in regulating DNA replication initiation at the rDNA locus in budding yeast.
• To understand the interplay between Rif1, PP1/Glc7 phosphatase, and other factors like Sir2 in rDNA replication control and genome stability.

Main Methods:

• Gene deletion studies (rif1Δ, sir2Δ, MRX, Ctf4-Mms22, Fob1, Tof1/Csm3).
• Analysis of rDNA replication intensity and repeat instability.
• Assessment of cell viability and synthetic growth defects.
• Investigation of replication fork dynamics and checkpoint activation.

Main Results:

• Rif1, in complex with Glc7 phosphatase, inhibits DNA replication initiation at the rDNA locus.
• Loss of Rif1-Glc7 activity increases rDNA replication and instability, similar to Sir2, suggesting a shared pathway.
• Rif1 deficiency exacerbates synthetic lethality with mutations affecting replication fork stability, particularly near the rDNA replication fork barrier (RFB).
• Rif1-Glc7 also regulates origin firing outside rDNA, preventing DNA replication checkpoint activation.

Conclusions:

• Rif1-Glc7-mediated repression of origin activation is crucial for preventing deleterious accumulation of stalled replication forks at the rDNA RFB.
• This mechanism is vital for maintaining genome stability, especially in repetitive regions.
• Findings have potential implications for understanding genome stability in metazoans with extensive repetitive sequences.