Replication in hydroxyurea: it's a matter of time

Area of Science:

• Molecular Biology
• Cell Cycle Regulation
• Genomics

Background:

• Hydroxyurea (HU) is a known inhibitor of DNA replication, impacting both elongation and initiation phases.
• HU triggers the intra-S phase checkpoint, a cellular mechanism that monitors DNA replication.
• Prior studies in budding yeast indicated that HU, under short exposure, inhibits initiation at late S phase origins.

Purpose of the Study:

• To investigate the genome-wide effects of extended hydroxyurea (HU) exposure on DNA replication origin activation.
• To determine if HU specifically excludes initiation from late S phase origins.
• To revise the model of the intra-S phase checkpoint response to HU.

Main Methods:

• Microarray experiments were utilized to monitor the activation status of all replication origins.
• Analysis focused on the temporal progression of DNA synthesis under extended HU treatment.
• Budding yeast was used as the model organism.

Main Results:

• Genome-wide DNA synthesis and origin activation patterns under HU treatment mirrored those without HU, albeit on a delayed timescale.
• No specific exclusion of initiation from late S phase origins was observed.
• All temporal classes of replication origins were affected, but their activation sequence remained consistent.

Conclusions:

• Hydroxyurea (HU) treatment results in a slowed progression of S phase rather than a specific blockage of late origin firing.
• The temporal program of replication origin activation is maintained, despite significant delays, under extended HU exposure.
• A revised model is proposed where the intra-S phase checkpoint orchestrates a slowed, but ordered, replication process in response to HU.