A yeast origin of replication is activated late in S phase

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Understanding the regulation of DNA replication timing in eukaryotes is crucial for comprehending genome stability and cell cycle control.
• Large chromosomal domains are known to replicate late in S phase, but the underlying mechanisms remain largely unknown.

Purpose of the Study:

• To investigate the mechanism responsible for the late replication of telomere-adjacent DNA in the eukaryotic chromosome.
• To determine whether delayed replication is due to slow replication fork progression or late activation of replication origins.

Main Methods:

• Utilized two-dimensional gel electrophoresis to identify and analyze active origins of replication.
• Performed kinetic analyses to measure the rate of replication fork movement in specific chromosomal regions.

Main Results:

• Identified a 67 kb telomere-adjacent region on chromosome V in Saccharomyces cerevisiae that replicates late in S phase.
• Confirmed that ARS501, an ARS element within this region, functions as an active origin of replication.
• Demonstrated that replication fork speed in this late-replicating region is comparable to early-replicating regions.

Conclusions:

• The delayed replication of this chromosomal region is primarily caused by the late activation of its replication origin (ARS501).
• These findings support the hypothesis that temporal regulation of origin activation dictates the pattern of early and late replication observed in eukaryotic chromosomes.